Transitioning to LiFePO batteries

LiFePO4 Battery on shelf, during installation

 

After doing my most recent research, I decided to replace the faltering AGM coach batteries with a LiFePO4 battery.  The decision was the easy part. Next came selecting a battery, installing it and integrating it into the existing Roadtrek 12VDC system.  I also have a solar system and de-sulfating controller.  Such a controller is not recommended with the LiFePO4.

The battery can be mounted in any position, and the space available provided two options.  I decided to go with terminals up. I did elevate the battery slightly by resting it on plywood.  It has a metal case and I don't want it sitting in water.  I've never had an issue with water in the battery pan but I don't ford streams or drive through flooded underpasses. There is always a first time.

The new battery will use the existing shunt and power wiring in the compartment.  The integration of other components did require some additional work on my part. I didn't want to make alterations to the existing wiring of the coach: no shortening or removal.  I wanted the wiring to be recognizable to a technician familiar with the Roadtrek or a future owner.  I also wanted to provide the ability to transition back to AGM batteries at some future time, although I don't expect to do that.

Maintenance Free LiFePO4 batteries?

There are limitations with any coach battery and LiFePO4 batteries have their own.  I decided to address these in my installation. 

It is true the LiFePO4 batteries are "maintenance free".  One significant advantage over other battery types is the internal, electronic battery management system (BMS) which is there to protect the battery.  (See Note 1).

However, to achieve optimal battery life (4000+ cycles) it must be operated within the design parameters.  That may require some external hardware.  I concluded that in my Roadtrek, replacing AGM batteries with LiFePO4 is not quite "plug and play" or "drop in and forget". 

Integrating the various 12VDC Components - a List

The LiFePO4 batteries aren't simply a "drop in" proposition. Here are the things I considered:

1. Tripp-Lite charger/inverter is to remain in place.
2. Retain Tripp-Lite 750W inverter function (~59A at 12.8V).
3. Make the provision for a future LiFePO4 charger. 
4. Solar charging system - update to compatible LiFePO4 controller.
5. Upgrade the battery manual disconnect.
6. Retain existing volt-ammeter and shunt.
7. Add a low voltage automatic disconnect to enhance the BMS cutoff (to preserve the battery).
8. Add battery compartment supplemental AC/DC heat to extend charging time.

Low Temperature Battery Considerations

One of the issues with the LiFePO4 batteries is their intolerance to cold.  The BMS will not allow charging if it determines that the battery internal temperature is at 32F or below.  Power output will vary with ambient temperature, but not as much as with the AGMs I'm replacing.   

High ambient temperature may accelerate the aging of the battery while low temperature may reduce output power capability. In general LiFePO4 batteries perform better at low temperatures than do the AGMs I'm replacing. 

I decided to install the battery in the unheated compartment where the AGM batteries were installed.  Minimal 12VDC power wiring changes would be required.  In that location the battery will be exposed to freezing temperatures at any time the outside ambient is below freezing.  Of course, I do have the option of relocating it to the interior of the coach at some time in the future.

Keep in mind that if stored outdoors all Class B's will have their interior temperature decrease to below 32F in fall and winter if the vehicle is north the freeze line. In cold weather the coach interior will be at cold until it is warmed by running the engine.  So too will any batteries stored within.  If the coach is parked in the sun the interior may be warmer than outside. The Roadtrek coach battery can be discharged when cold, but the LiFePO4 battery can't be charged until the battery internal temperature rises above 32F.

I concluded that to store the Roadtrek in winter, if that is necessary below freezing conditions that I'll simply remove the batteries.  If I use it at below freezing temperatures some supplemental heat to warm the batteries would be desireable. That will extend the charging of the LiFePO4 battery as weather cools.  

I do realize that at some point the ambient temperature will be so low as to nullify the supplemental heat and the BMS will prevent charging the battery. I don't expect to encounter that situation. LOL.

Some batteries are available with internal 12V heaters but that draws down the battery in cold weather if the vehicle is not running and not connected to shore power.  Furthermore, if this is an internal battery function and can't be controlled by the user it simply runs the battery down faster if off the grid.  In my opinion that's undesirable in a RV.

I'll be installing both 120VAC and 12VDC supplemental heaters, which I can control.  I'll be monitoring the compartment temperature to get some data about the effectiveness. 

Avoid Over Charging and Over-discharging

Another issue is the possibility the internal battery cells can be damaged if they're discharged below a certain threshold. That low point is approximately 5 percent of total capacity. If the cells are discharged below this threshold their capacity can be permanently reduced.  The BMS will protect the battery, but at too low a threshold to preserve optimum life. 

The solution is an external, automatic cutoff or a low voltage alarm (or both).  

I have installed a low-voltage automatic cutoff. 

Three methods of Charging

I have three methods for charging the batteries in my Roadtrek. Ideally, each method would provide the appropriate charging voltage and current for LiFePO4 batteries, but they don't:

1. Tripp-Lite charger inverter using 120VAC power (3-stage voltage and current control).
2. Solar using solar panels and a controller (voltage and current control).   
3. Engine alternator (simple voltage regulation, no control).

The first two methods can be adjusted to adhere to the battery charging specifications.  The alternator has no such adjustments.  To avoid over-charging the coach batteries I can use the battery separator to disconnect from the alternator and rely upon solar charging.  Alternately, a DC-to-DC charging system could be installed.  There are practical limits to how much I'm willing to spend on this.

External low voltage disconnect - Details

The battery manufacturer recommends that an external low voltage disconnect be used.  The manufacturer suggests 11.2V as the disconnect point.  

• Battery low voltage disconnect < 11.2V

Such a voltage represents about 5% battery capacity remaining.

There are a couple of methods to achieve this:

1. Manual switch.
2. Automatic switch or relay.

It is true that the battery management system will protect the battery from complete discharge. However, 10.4V is about 2% battery capacity.

• BMS Low-Voltage disconnect <10.4V

In general, a battery constructed of Grade A cells can probably achieve the specified cycles if the battery is operated within the manufacturer's parameters.  Discharge to very low voltage is to be avoided. 

A battery low voltage alarm is a possibility, too.  For example:

• Battery low voltage alarm < 11.8V

Such an alarm would occur when the battery capacity has decreased to about 8%. 

Adjusting to a new reality.  As I use the LiFePO4 battery I'll have to adjust.  For one thing, the output voltage versus State of Charge is different than the AGMs.  The new battery is more stable than the AGMs.  After charging, and intermittent use for a week, the battery voltage has decreased by 0.06V.  This battery seems to be much "stiffer" than the AGMs.  This may change as the battery ages and capacity decreases to about 80%. 

State of Charge - SoC - Details

I provide a typical chart later in this post.  State of Charge (SoC) is a very useful battery measurement. It states the present, actual capacity of the battery compared to its total capacity. 

State of Charge is a percentage: 

• 100% SoC means the battery is fully charged, new and undamaged.
•  0% means fully discharged. 

 SoC is calculated this way: 

• State of charge (%) = Remaining Capacity (Ah) / Total Capacity (Ah).

LiFePO4 batteries are chemical devices and so they operate similarly to the AGM lead acid batteries we are familiar with. There are several SoC values to keep in mind.  These are the absolute minimum SoC, the preferred SoC and the actual SoC.  

Absolute minimum SoC is the most discharged state with the lowest possible terminal voltage that doesn't destroy the battery.  For my battery this is 10.4V.  However, discharging to such a low voltage will diminish the capacity and useful cycles of the battery. 

For maximum battery life, only discharge it down to the Preferred level, but no lower. Hmmm, that seems reminiscent of the recommendations for AGM lead-acid batteries, doesn't it?  Here are the three values:

• Alarm and recharge at <11.8V (the Preferred minimum state of charge, 8-10%). To maintain reasonable battery longevity and performance do not discharge below this value.
• External battery cutoff <11.2V (Actual minimum state of charge, 5%). This is the realistic minimum.  The battery can be discharged to this state, but some battery degradation and performance will occur is the battery is operated this way.  This discharge level is a trade-off between available power and battery life.
• Battery BMS low voltage cutoff <10.4V (Absolute minimum state of charge, 0%). This is approaching the point of battery destruction.  The BMS will stop battery discharge when this state is reached. 

LiFePO4 Terminal Voltage and SoC

A typical 12V LiFePO4 battery is constructed of four cells called a 4S battery pack. The battery output voltage decreases as the batteries discharge and remaining capacity decreases.  A typical 12.8V battery output will vary from 13.8V to as low as 10.0V (completely discharged).  

The nominal output voltage is 12.8V.  There are differences among manufacturers, but here are typical voltages:

• Absorption Voltage (charging) 14.4-14.6V  (3.6-3.65V per cell).
• Float (fully charged) 13.6-13.8V (3.4-3.45V per cell).
• Full discharge 10.0V (2.50V per cell).
• Nominal voltage 12.8V (3V per cell)

The terminal voltage will decrease as the battery discharges and the capacity diminishes.  To get an accurate reading of SoC the battery must be rested.   Here's a typical chart. You will note that the battery output voltage is reasonably flat throughout the useable discharge cycle, from about 100% down to 10%:

• 13.6 V = 100% SoC (Fully charged)
• 12.1V  = 10% SoC (Preferred minimum)
• 1.5 V output decrease from Fully charged to minimum SoC.

LiFePO4 Capacity versus Battery Voltage 

Note:

1. There are different battery constructions out there.  Some have as many as 8 internal cells. This is an evolving and improving technology. Low temperature automatic protection by the BMS and internal 12V heaters are relatively new.  Some batteries are well constructed internally, and some are not. Some have steel cases, while most have plastic. Prices range from about $325 to $900 for a 12V, 100Ah battery.

(c) N Retzke 2022

Lithium-Ion Battery Update - I changed from AGMs

 

100 Ah LiFePO4 Battery

During the FMCA Rally, I had an opportunity to attend a battery seminar and also discuss features and current prices with several battery vendors.   In February 2015 I posted here about Lithium-Ion LiFePO4 batteries. In that post I said: "a similarly rated lithium battery system will probably deliver about 45% more power than a similarly rated AGM battery system, and it will probably do so for at least 6-7 years."  

Here's a link to the earlier post:

Are Lithium RV Coach Batteries Expensive?

In August 2017 I posted this comparison:

Comparing AGM and Lithium RV Battery Systems

In March 2018 I posted this:

Lithium Battery and RV DC Power System Developments

In October 2019 I posted an update:

Coach Batteries - AGM versus Lithium-Ion Update

The battery seminar was cancelled. I'd been hoping to get current information and insights. I discussed with FMCA and advised them that I could provide a 1-hour presentation.  For one thing, I have nothing to sell and I'm very familiar with what's available, the costs, as well as the pros and cons of each battery type. However, there were several battery vendors at the rally, and I had the opportunity to talk to Battle-Born, RVConnection, etc.

One of the Roadtrekkers brought up coach batteries in a conversation and told me he was interested in building a LiFePO4 battery.  That piqued my interest.  After the rally I did some additional research.  

My AGMs were installed in January 2017.  They are 5-years old.  I do test the capacity of my batteries from time to time and I had determined it was about time to replace, as the capacity has diminished, which is normal. BTW, using the Roadtrek LED indicator isn't very useful for this.  I measure the battery voltage under load and monitor the decrease in voltage over time under load.  By discharging the battery at a constant current, I can observe the decrease in battery voltage.  That's how I know the battery condition.  I admit it is a rough estimate, but adequate for my needs.  

Some Roadtrekkers use the LED L-F-G-C volt indicators.  I don't. The "G" indicator is illuminated at about 11.9V and above.  My AGM batteries are at 25% SOC at 11.9V OC (Open circuit), which is below the minimum 50% state of charge necessary to achieve rated life. 

Is it time to change to Lithium?

I had once again been thinking about switching from AGM coach batteries to Lithium-Ion.  I too was interested in building my own batteries.  I decided to check prices, which have changed significantly in the past couple of years.

What I discovered was I can purchase a complete battery for about the same price as building one.  In one of those oddities, the price of the components is now nearly equal to the price of some of the assembled batteries; I guess the marketing people in the factories in China figured it out. A year or so ago the parts were less costly than the batteries, but no longer. This is not surprising because a 12V LiFePo4 battery requires these components:

• (4) 3.2V LiFePO4 Cells.
• (1) Battery Management System (BMS).
• Screws, buss-bars, wire and terminators for the BMS.
• (1) Case, which is sometimes called a Rack, to hold the cells.

Add up the cost of all of the above and compare to the cost of some of the batteries available. At present there isn't much of a difference.  I won't put the component numbers here. However, I decided that while assembling my own battery would me a fun exercise, there was no financial incentive for me to do so.

Note: There are some very low-cost Lithium LiFePO4 batteries available. I've seen prices as low as $300 for a 12V 100Ah battery. However, the price range is from $300 to $900.  I decided to do research into testimonials and specific battery reviews as part of the selection process. I also decided to make a simple specification so I could do a reasonable comparison. 

Be aware that there are different grades of 3.2V LiFePO4 cells; A, B, C, etc. Those cells are assembled in a case with a battery management system (BMS) to make a 12V, 24V or 48V battery.  Grade A cells are more expensive than Grade B cells. Grade B cells are characterized as "unqualified" at manufacture.  Maximum benefit is achieved from a LiFePO4 battery constructed from Class A cells.  But different manufacturers use different standards.  So, a Class A cell from one manufacturer may be the equivalent of a Class B from another.  Confusing, isn't it?  That's why it is a good idea to purchase a battery from a known manufacturer (or assembler) who provides a proper warranty. 

Battery Prices and available capacity:

One thing that is unchanged is the price differential of AGM batteries versus LiFePO4. True, the lowest priced lithium batteries are competitive with AGMs, but may not offer features or warranties. Determining battery quality isn't easy. I decided to avoid the lowest cost lithium because there are different quality levels in the cells.

Bottom line is, the AGMs are less costly, out-of-pocket.  However, if one compares the capacity of the batteries and charge-discharge cycles, the LiFePO4 offer superior performance. 

Furthermore, because we seldom boondock, I don't need a lot of Ampere-hours from the batteries.

Here's an "out of pocket" price comparison.  I priced an inexpensive 12V AGM battery as follows:

• AGM (lead acid) = $219 + shipping + tax
• LiFePO4 = $569 + shipping + tax

There is a capacity difference and that should be considered.  Considering how I use my Roadtrek, the fact that I do have solar available, and I have an Onan generator, I really don't need two 100 Ah Lithium batteries. However, a single 110Ah AGM could only provide 55Ah which is not sufficient. As a consequence, I need to compare 220Ah AGM to 100Ah lithium.  This would be adequate based on available capacity:

• (1) 220Ah AGM = 110 Ah available (50% maximum discharge)
• (1) 100 Ah LiFePO4 = 80 Ah available (80% maximum discharge)

Battery price per Watt-hour (Wh):

The following is a simple cost comparison and doesn't consider lifespan, number of cycles or battery performance degradation. In fact, it would be more accurate to use 50% capacity for the AGM and 80% for the LiFePO4.  Discharging below those levels can ruin the AGM and may reduce the lifespan of the lithium battery.

For example, one 12V, 100 Amper-hour (Ah) assembled LiFePO4 battery which has acceptable specifications has a price of $569 plus shipping plus tax. That's $0.44 per Watt-hour (Wh), as follows:

$0.44 = $569 / (12.8V x 100 Ah)

A 12V, 100 Ampere-hour (Ah) AGM battery has a minimum price of $219.  That's $0.18 per Watt-hour (Wh):

1 battery $0.18 = $219 / (12.5V x 100 Ah)

2 batteries = $0.36 per watt-hour

If I were to purchase a single 206 Ah LiFePO4 battery, the cost per Wh would be less, while the price of two AGMs would be twice the capacity for twice the price:

$0.39   = $1,029 / (12.8V x 206 Ah)

Prices above are "raw" which is to say, a simple cost per Wh.  However, if we consider the life of the batteries, the numbers change.  An AGM battery can provide 500 charge-discharge cycles. A Lithium-Ion battery can provide 4,000 charge discharge cycles. The LiFePO4 battery can be repeatedly discharged 80% and the AGM 50% to provide this cycle lifespan.

Realistic battery price per Watt-hour (Wh):

In fact, the AGM battery I would be inclined to purchase would be the Deka 8AGC2.  This is a 220Ah  6 V battery which closely matches the original furnished with the Roadtrek. Two would be required to get 12V, but at 50% useable capacity they would provide 110Ah at 12.5V. The cost each is $300 + shipping + tax. This is the realistic AGM battery cost per Watt-hour:

AGM batteries: $0.44 = $600 / (12.5V x 110 Ah)

One 12V, 100 Amper-hour (Ah) assembled LiFePO4 battery which has acceptable specifications has a price of $569 plus shipping plus tax. It has a 80% useable capacity, 80Ah. That's $0.56 per Watt-hour (Wh), as follows:

100Ah Lithium: $0.56 = $569 / (12.8V x 80 Ah)

The AGMs when new can provide energy at a lower cost than the Lithium.  However, the Lithium batteries will provide more power over their lifetime because they can tolerate greater number of charge-discharge cycles.

Comparing Charge-Discharge Cycles

If we consider charge-discharge cycles, then these batteries can provide these Wh over their lifespan:

Lithium:   3,840 KWh = 4000 cycles x 1200 Wh x 0.8

AGM:      300 KWh = 500 cycles x 1200 Wh x 0.5

As can be seen above, the lithium can provide 12.8 times greater power (3840 / 300) over its lifespan.  Considering battery lifespan, the lithium batteries are substantially less costly.

Cost over the life of the batteries

If I take the initial cost and divide by the number of useful years, I can arrive at an estimated cost to own per year.  I am using my experience with my AGM batteries, which provided 5-years of useful life in my Roadtrek. For comparison I'm using the warranty period of the LiFePO4 batteries. Note that the warranty is 7 years but can be extended to 10 years.  To make this comparison, I'm using two AGM's (100 Ah useful) and one LiFePO4 (80Ah useful).  I'm ignoring shipping and tax, and I am assuming that the existing Tripp-lite charger/inverter will work with both batteries. That's the configuration I'm considering.

Lowest cost AGM:  $88 per year = (2 x $219) / 5 years

Deka AGM: $120 per year = (2 x $300) / 5 years

LiFePO4: = $82 per year = $569 / 7 years

If one can get a 10-year warranty for the LiFePO4 batteries, the cost per year is further reduced, and the Lithium battery is less costly than the AGM:

LiFePO4: = $57 per year = $569/10 years

Advantages and disadvantages

Lithium LiFePO4 batteries have these characteristics:

1. Can be repeatedly discharged to 80% with no reduction in battery life. In other words, a 100 Ah battery (1200 Wh) can provide about 960 Wh safely without decreasing battery life. A similar AGM battery should not be discharged more than about 50% repeatedly.  The AGM can provide about 600 Wh, which is 63% of the power provided by the LiFePo4 battery.
2. The Lithium can be charged-discharged about 4,000 to 8,000 times, or cycles.  The AGM battery, if discharged repeatedly to 50% can be charged-discharged about 500 times, or cycles. The lithium can be charged-discharged at least 8 times more cycles than the AGM.
3. The Lithium battery provides power at 13.2VDC.  This may gradually decrease to 13.1V when discharged to 40% capacity.  At 20% remaining the battery will be about 12.9V.   The AGM begins at about 12.9V and decreases to about 12.3V at 50% state of charge.  At 20% remaining the battery voltage will be about 11.7V.  Actual output may vary by manufacturer.
4. The Lithium cannot be charged at temperatures below 32F (0C).  To do so the battery will be ruined.  Using Lithium batteries in below-freezing conditions takes some forethought.  However, they can be discharged at any temperature. Adding a battery heater can solve this problem.
5. The LiFePO4 battery may be mounted in any position (but check with specific manufacturers for their limitations and recommendations).

My Specifications  & Tripp-Lite Charger-Inverter Settings

To make an apples-to-apples comparison of LiFePO4 batteries from various suppliers I had a simple specification:

1. Minimum 4,000 cycle life.
2. Internal Battery Management Systems (BMS).
3. Low temperature cut-off to protect the batteries.
4. Over charge & over discharge protection
5. Over current & short circuit protection.
6. High temperature disconnect.
7. Storage as low as -22F. Discharge temperature range -22°F to 140°F.
8. Charging temperature range 32°F to 140°F.
9. Charging Current range 0 to 20A (maximum 50A).
10. Maximum output 100A.
11. Be compatible with my Tripp-lite charger (14.4V Charging Voltage and 13.5V float, maximum 45A charging current). - Note 1, 2, 3 below.
12. A minimum 7-year warranty.
13. Prefer a removeable cover and replaceable BMS, but not mandatory.
14. Blue-tooth (r) communications optional.

Note 1: The Tripp-lite has two charging settings for two different types of batteries:

• "Wet Cell (vented)" (DIP Switch A1 in the DOWN position) and
•  "Gel Cell (sealed)" or AGM (DIP Switch A1 in the UP position).  

Note 2: The Tripp-lite has three stages for charging: BULK, ABSORPTION and FLOAT.  The "Absorption" and "Float" stage voltages are adjusted by selecting the battery type:

• Wet Cell: 14.4 VDC "Absorption", 13.5 V "Float".
• AGM: 14.1 VDC "Absorption", 13.6 V "Float". 

Tripp-lite BULK Stage: In this stage, the battery is brought up to about 80% capacity using a constant charge current; the charge voltage can vary in this stage.

Note 3: The Tripp-lite has two charging current rates:

1. 11 Amperes (DIP Switch B4 in the UP position).
2. 45 Amperes (DIP Switch B4 in the DOWN position).

Battery Selection & Sizing Considerations 

To choose LiFePO4 batteries it would require these decisions:

• Choose (1) or (2) 100Ah batteries (total 100Ah or 200Ah capacity; 80Ah or 160Ah useable).
• Or choose (1) 200Ah battery (160Ah useable).
• Determine mounting location: (1) or (2) 100Ah mounted outside or (1) large 200Ah battery mounted inside the coach (the 200Ah battery is too large for the Roadtrek battery tray). Inside mounting would add cost, as additional 6AWG wiring would be required.
• A single 100Ah battery could provide 20A for 300 minutes (about 240W for 5 hours).
• A 200Ah battery could provide 20A for 600 minutes (about 240W for 10 hours).
• The Tripp-lite inverter is rated 750W continuous.  Ignoring losses, the inverter input for 750W AC output would be about 60A at 12.8 VDC.  The battery should be capable of providing that current output.  The inverter can provide 150% output for a short period of time, so a battery capable of 100A output would support that. Of course, higher battery current decreases available battery time; 60A output could deplete the 100 Ah battery within 100 minutes.

To protect the battery, a low voltage cut-off device at 11.2V is recommended.  The BMS of the battery I am considering will cut-off at 10.4VDC. However, this very low cut-off voltage may reduce battery life.  An in-line fuse is also recommended.  I do have a digital voltmeter installed, so I can rely upon that at the lowest cost approach.  Keep in mind that battery voltage is an indicator of the battery capacity, but the battery must be at rest for this method do be accurate.  "At rest" means nothing drawing a load.  In my Roadtrek I can use the battery voltage as an indicator if 1) The chassis/coach battery separator is in the "off" state, 2) the battery disconnect is "off" and 3) the inverter is "off".  About 15 minutes after disconnecting the LiFePO4 batteries I'll consider the voltmeter reading to be indicative of the battery capacity.  

Because the LiFePO4 can't be charged below 32F, mounting inside the coach has an advantage. The interior coach temperatures can be maintained above 32F while the coach is in use. However, if the battery were in the outside compartment a heating pad could be attached to the battery to provide some supplemental heat in the winter, thereby keeping the battery or batteries above freezing. It would be my preference to mount outside to conserve interior space.   The heater will add cost. 

Notes: 

1. Certain RV organizations including FMCA and Escapees may offer price discounts to members for specific batteries.
2. Certain manufacturers offer batteries which have internal heaters and have blue-tooth (r) communications.  However, this is at greater cost.
3. The Roadtrek battery tray is outside of the coach.  Care must be taken to assure that the LiFePO4 batteries mounted within stay dry.
4. The charging requirements of the battery selected must be compared to the capability of the Tripp-lite charger/inverter to assure compatibility.  Otherwise, a new charger and inverter would be required.  
5. I decided to purchase a single 100AH SOK battery pictured at the beginning of this post.  If purchased directly from the U.S. supplier, the warranty is extended from 7 years to 10 years.  My cost for (1) battery was $624.93.  This included tax and shipping.
6. If I decide to add a thermostat and 12V heater to keep the battery warm, my out-of-pocket additional expense would be about $40 (fuse, pad, thermostat).  A second 120VAC 84W heating pad with internal 45F thermostat is about $39. Why two? Well, if I decide to winter camp on 120VAC, I can heat the battery using shore power or the generator.  Alternately, I can use the chassis alternator to heat the battery using 12VDC while the Roadtrek is in motion or I can use coach 12VDC to maintain the LiFePO4 above freezing.  I have not purchased any parts, but I do anticipate installing at least the 12V heater.
7. My Solar system will work with the LiFePO4 battery.
8. Low voltage disconnect at 11.2V is recommended for maximum battery life. If I want to add an automatic cut-off that would be at additional cost. I currently have a DC display with alarm. Here's the post link:  New Voltmeter-Ammeter-Wattmeter for AGM batteries  

(c) N. Retzke 2022

Coach Batteries - How to get the most out of them

DC Voltmeter and Ammeter to monitor the coach batteries.
I added this to improve upon the Roadtrek LED battery indicator.
If left on, it also provides a power reading and energy consumed.

Roadtrek L-F-G-C battery display -
4 LEDs lit indicates charging or fully charged.

The post points out what I've learned  about my AGM batteries including limitations of the L-F-G-C  battery display which is simple to read but can be misleading, as I discovered.

How do we use the Roadtrek if we're not in a campground? This is important because it influenced our battery decision. We do overnight in the Roadtrek off of the grid, but we don't do a lot of boondocking. If the temperatures are above freezing but cold we may run the generator and the heat pump. However, G and I have also slept in the Roadtrek in sub-freezing temperatures while off the grid and below the limit for the heat pump. We will then run the propane furnace if necessary and that requires 12VDC.  If temperatures dip into mild sub-freezing overnight and we haven't winterized we will run the hot water heater on propane and the furnace. If we are on propane I don't think it is practical to run the generator continuously overnight and we usually don't. We rely on battery power.

What I discovered. I did not understand the limitations of that L-F-G-C Battery indicator and learned that "F" or "Fair" is really "Poor" because the batteries may be nearing depletion at that point.

I also learned that the Inverter Off-On switch didn't always turn off the inverter function of the Tripp Lite inverter/charger; that was a switch malfunction. It caused unexpected battery depletion.

I realized I had been mis-using my batteries. I didn't understand that the entire 220Ah or rated battery capacity is not available unless I want to seriously reduce the lifespan of the batteries. I also learned that repeatedly using the batteries below the "F" Fair indicator and until only the "L" or "Low" indicator was the only one illuminated was not good for the batteries, if I want longer battery life. My lack of understanding coupled with an inverter switch problem led to the early demise of my first set of AGM batteries.

I've learned about AGM batteries and when I replaced them I also investigated Lithium-Ion batteries (LiFePO4). I'll point out what I discovered about the AGM batteries in this post, but first, I decided that I would continue with AGMs because:

• 220Ah AGMs are sufficient for my use (approximately 110Ah to 170Ah useable - explained in this post).
• I have an Onan generator which I can use to provide power for coach appliances and charging.
• I was concerned about the low temperature charging restrictions of LiFePo4 batteries because my AGMs are mounted outside in the rear of the coach. That is the location I would use for LiFePO4 replacements.
• I did not want to open my wallet for the more costly LiFePO4 batteries.
• I decided to add a small 50W portable solar panel with de-sulfating 180W controller to help charging of the batteries. I concluded this was a better use of my money as compared to the LiFePO4 batteries. I may eventually put a 100W panel on the roof.
• I decided that adding a good DC voltmeter/ammeter to monitor the batteries would assist me in using them and avoid the earlier problems.
• There have been improvements in technology, and who knows, I may change my mind in 2-5 years.

This post is about a few things that may help you improve the life of your AGM batteries. 
I include a typical 12VDC energy audit at the end of this post.

My 2013 210P Roadtrek has two 6-Volt AGM lead-acid sealed batteries rated 220Ah. I use these on our treks in both warm and cold weather. We don't boondock a lot, but we do spend overnights off the grid. The numbers in this post are with those batteries in mind.

Some things I have learned
These lead-acid batteries can provide 4-6 years of good life, and sometimes more. But how they are used is a significant factor and determines how long they provide good service. Here are a few things to be aware of, and more on what the indicator in the Roadtrek is attempting to display and how it relates to what we observe with our batteries.

I don't think it is possible to reverse the aging of these batteries. It is possible to damage them.

How the batteries are used and discharged/charged is probably the single greatest determinant of how long these lead-acid batteries can provide good service. Battery life is determined by age and these cycles. We sometimes don’t get the life out of the batteries we may expect. I have two 6-volt AGM batteries. They are wired in series to provide 12V DC and can provide a maximum of about 220Ah (Ampere-hours).

What are DC Watts and Volts and Amperes?
These are important because they relate directly to our batteries. If we know the amperes our appliances and lighting are using we can estimate how long on a charge we can run them.

You can skip this and move on to the next section, but I think you will want to read this before you do an audit of your DC appliances and get a better idea of how much battery power you are using.

1. Watts are Volts multiplied by Amperes. In our Roadtreks with 12V AGM batteries:

• 12V x Amperes = Watts; for example 12V x 5A = 60 Watts.

The battery voltage does stray but for doing calculations using 12V is handy.

1. Because we know watts and the voltage, we can calculate Amperes. For example:

• Watts divided by volts = amperes. A 100 watt DC appliance: 100W/12V = 8.33A

An Ampere-hour (Ah) is a measure of amperes used per hour. Batteries are rated in Ampere-hours.

• An Ampere-hour is using one ampere continuously for an hour: 1A x 1 hour = 1 Ah

Ampere-hours let us determine how much battery capacity is being used. For example, let's assume we three things that are using DC electricity:

• 1.0A lights
• 0.8A charging phone
• 2.6A furnace and fan.

If we add these up, we can see how many Ampere-hours they would use in one hour:

• 1.0 + 0.8 + 2.6 = 4.4A
• 4.4A x 1 hour = 4.4Ah

If we multiply by the number of hours these appliances and lights are "on" we can determine how many Ah will be used in total, and as you will see this is useful for estimating how long our batteries will provide us with electricity between charges.

For example, let's say we left those appliances and lights on overnight, for 8 hours. Here is how much battery capacity they would use:

• 4.4A x 8 hours = 35.2 Ah

Later in this post I provide some estimates which can be used to determine how long your batteries could last when providing DC power.

What use is knowing Ampere-hours? Ampere-hour (Ah) rating of a battery is a measure of how many amperes a battery can provide when discharging. One Ampere-hour is one ampere for one hour.

Unfortunately, a battery rated 220 Ah cannot provide 220 Amperes continuously for one hour.  In watts that is 220 A x 12V = 2640 Watts total.

A 220 Ah AGM battery cannot be used that way.  The more we attempt to pull from our batteries, the less Ah they can provide in a short period of time. I'm using the data provided by the manufacturer of my batteries, which is relative capacity. Relative capacity takes into account "battery fade" which normally occur to batteries as they age and are used:

1. To get good battery life, these batteries should not be repeatedly discharged more than about 50%, and when discharged should be immediately recharged. In other words, one cannot get 220Ah out of these batteries if we want good life from them.
2. A 50% discharge of 220Ah is 110Ah that we can use. The batteries must then be recharged. AGM batteries discharged repeatedly 50% and then recharged can provide about 1200 charge-discharge cycles. That’s the service life. Keeping batteries fully charged and not storing them partially discharged also is an aid to improved service life. Temperature also impacts service life, and temperatures above 77F reduce battery life.
3. These batteries can be discharged repeatedly by 80% but that will reduce the life. A 80% discharge of 220Ah is 176Ah that we can use. AGM batteries repeatedly discharged 80% can provide 700 charge-discharge cycles. That is much lower than the number of cycles if we only discharge to 50%.
4. Many battery manufacturers use a 20 hour rating for batteries. That is a more realistic and useful measure of battery capacity. For example, my AGM batteries are rated 220Ah, which implies continuous 220A for one hour. The actual 1-hour rating of the batteries is only 130A.
5. The battery can, however provide a total of 220Ah over 20 hours of discharge.  That is a continuous 11 amperes for 20 hours.  But we should only go for 50% which is 5.5 A for 20 hours. This is to get better battery life. 
6. Over 10 hours, a typical night, the battery can provide a total of 210Ah according to my battery manufacturer. In other words it can provide 210Ah/ 10 hours = 21 amperes continuously each hour for that 10 hours. But, if we only discharge the battery 50%, of the 220Ah full rating, that implies about 110Ah/ 10 hours or only 11.0 amperes continuous discharge for 10 hours.
   
   Conclusion: Over a typical night, my batteries could provide 11.0 Amperes each hour and provide good service life.
7. These are the characteristics of the batteries in my Roadtrek when they were new. This capacity diminishes with battery age and use. 
8. There are differences between manufacturers, so it is best to check the specifications for your batteries.

What are cycles?

1. What does 1200 charge-discharge cycles mean? That's the number of times we can discharge and immediately recharge the batteries. For example, if you discharged the batteries to 50% and then fully recharged them once a day and every day, they could have a useable lifespan of 1200 days. 1200 days/365 days per year= 3.2 years battery life.
2. If you did this every three days, then we would complete a cycle every three days, or 365/3 days = 122 cycles in a year.  1200 cycles/122 cycles per year = 9.8 years life.
3. However, because of other factors including temperature, length of time the batteries sit in a partially discharged state, battery age, etc. it is unlikely we will ever achieve this in our Roadtreks.  The manufacturer’s battery data is based upon ideal situations, including a temperature of 77F

What occurs as batteries age? As batteries age there are internal changes and that reduces the capacity. For example, after 600 cycles of charging and discharging the battery to 50% what occurs?

1. As the batteries age, even under ideal conditions, we may not get that 110Ah because the capacity of the battery diminishes as it ages. This is called battery fade. In other words the battery initially can provide 220Ah, but the actual capacity decreases over time.  We notice this as a more rapidly falling terminal voltage, which we can see on the Roadtrek L-F-G-C display, which spends less time in the “Good" area. In other words, the display falls from C to G to F more rapidly than one would expect. That is an indicator of aging batteries with diminished capacity. Eventually we decide that the batteries don’t provide us with enough power to get through the night or whatever while powering our devices. We then get new batteries.

What happens if we repeatedly discharge the batteries below 50%?

1. Frequently discharging the batteries below 50% will further reduce the service life. For example, we can repeatedly discharge them to 80% (20% remaining). If we do this,  the service life will decrease. My battery manufacturer states that discharging repeatedly 80% will reduce battery life to about 700 cycles. That is considered to be the lowest acceptable service life.
2. At 700 cycles if we discharge and charge every 3 days (122 times a year), the batteries will have a useful life of about 700 cycles/122 cycles per year = 5.7 years. But we must also consider the aging of the battery, temperature and so on. These also reduce battery life.

There is a trade-off.

1. We must decide between longer battery life, or more power from each charge, or a compromise. In practical terms we must choose between how long we want to power our DC appliances each time we discharge the batteries and how long a battery service life we want. We can’t get both maximum power for maximum time because the deeper we repeatedly discharge the batteries the shorter the service life. We notice this as how quickly the available power diminishes. Of course, we can replace the batteries every three years or so. That is a financial decision.

Does the Roadtrek “L-F-G-C” tell me when the battery is at 50%? The information I have about this is the “G” indicator is “ON” if the battery in my coach is above 11.9 volts, which is about 29% state of charge for my batteries.

1. If I use the "G" indicator and recharge the batteries when it goes out, then my battery manufacturer indicates that I can get about 800 cycles from my batteries if I discharge them to about 20-30% repeatedly.
2. Important Note: I have not verified the Roadtrek indicator with actual measurements comparing the battery voltage to the indicator LED thresholds (I use a voltmeter and no longer pay much attention to the indicator). I'm using published information and it is my understanding that the “F” indicator is “ON” if the battery is above 11.2V,  but the table for my batteries indicates a 0% Relative state of charge when the voltage decreases to 11.6V and completely depleted at 10.5 volts. The table provided by the manufacturer of the AGMs in my Roadtrek indicates 50% relative State of Charge = 12.35V and 100% State of Charge = 12.9 volts.  I’ve seen other AGM charts and those batteries were in the range of 11.66V (20%) to 12.05V (50%) to 13.0V (100%).

What else should I know about the Roadtrek “L-F-G-C” indicator?

1. It measures battery voltage. This is an approximate indicator. A battery will give two different voltage readings. One reading if it is being discharged; the another is if it has rested (no discharge) for about 6 hours.  The battery specification for “State of Charge” are usually for a resting battery. If a battery is discharged and then allowed to rest the voltage will usually increase. In other words, the battery may have more capacity remaining than the “L-F-G-C” indicator represents when we are in our Roadtrek and discharging the coach batteries.

What is the best approach for the batteries?

1. Use a voltmeter if we want a better idea of the condition of the batteries, so we avoid excessively discharging them. Avoid high temperatures because battery life decreases at higher temperatures.  Measured  life is usually at 77F and many batteries will lose half of their life if the temperature is 95F. Don’t charge if above 120F. Charge the batteries after every period of use. Don’t discharge more than 50%. All of these things improve the life of the batteries.
2. We can add a voltmeter in the rear cabinet of a 210P to monitor the voltage. 

3. 

   12VDC socket in the rear of my 210P

   
   

   

   Inexpensive 12VDC digital meter
   plugs into socket in photo above

   

   Inexpensive 10 inch Splitter Cable for 12VDC
   Use if we need two devices from a single 12VDC source,
   such as the photo of the cabinet, above. 

   
   

   

   Dual, fused splitter with digital voltmeter
   and USB sockets

   
   
   As battery capacity diminishes what does that mean in practical terms if I want to boondock? 
   
   1. There is a trade-off. Longer battery life, or obtaining more power from each charge. This is further complicated because as the batteries age, their capacity is diminished. The actual capacity of a 200Ah battery will gradually decrease to 190 Ah, 180 Ah, 170 Ah and so on. This is because the internals of the battery change as it ages. We usually notice this change because the voltage decreases more rapidly as the battery discharges. 
   2. The beginning voltage of a fully charged battery will be that of the charger which is about 14.7 volts, this is called “surface charge” and this charge dissipates quickly as we discharge the battery. Both good and faded batteries will usually show a "C" when on the charger, and immediately after they are disconnected.  That is deceiving and is not indicative of the actual state of the batteries.
   3. If an older 220Ah battery has a capacity that begins at 160Ah capacity then it won’t take very long to get to that 110Ah level which is the 50% capacity level of the new battery. We see this as a more rapid movement of the indicator as the indicator moves more rapidly from “C” to “G” to “F”.

Are there other things I should be aware of?

1.  Here is the short list. Batteries must be properly charged in accordance with the manufacturer’s instructions, automatic chargers are best. For golf cart batteries at 12V that usually means an Absorptive/bulk charge at 14.7 volts and a Float charge at 13.5 Volts. AGM batteries may be slightly different with an Absorptive/bulk charge at 14.4 volts and a Float charge at 13.5 Volts. My AGMs recommend an Absorptive/bulk charge range of 14.4-14.7V and a Float charge of 13.2-13.8V. Because the lead-acid batteries are chemical devices, there are other noticeable issues. 
2. Battery capacity is reduced at lower temperatures. A 200Ah AGM battery may have a capacity of only about 80% at 32F or 160Ah.  However, that is at a discharge of about 20Ah (about 4A per hour for 5 hours).If we increase the to 40Ah, the capacity reduces to about 70% or 140Ah. (That provides a rate of about 8A per hour for 5 hours). However, we still have to watch the battery voltage to determine the actual condition, or state of charge. We can’t simply watch a clock.
3. A 200Ah AGM battery is rated to provide that amount, 200Ah over 20 hours. It can provide 200Ah/20 hours = 10 amperes per hour continuously for 20 hours. But we would not want to exceed that 50% discharge limit if we want acceptable battery life.  In practical terms, a 200Ah battery should be considered 100Ah. if that is so, it can provide 100Ah/20 hours = 5 amperes per hour continuously for 20 hours.
4. If we increase the amperes used, then the time the battery can produce it will decrease. The same batteries will provide only about 170Ah over 5 hours, not the 200Ah rated over 20 hours. In other words, the more power we demand, the total amount decreases. That’s because these are chemical devices. If the batteries could provide 170Ah over 5 hours, that’s 170/5 or 34 amperes each hour at 100%. But if we allow only 50% discharge, we then can use only 34A x0.5 = 17 amperes per hour over the 5 hours. 17 amperes x 12 volts = 204 watts connected to the battery. 
5.  If we use an inverter to get 120VAC from our batteries, we need to take into account the inefficiency of the inverter. In other words, if we run a 200W appliance at 120VAC on the inverter, the amount of DC power going into the inverter is greater than the AC power coming out. Simply turning on the inverter uses power, perhaps as much as 200W. To maximize battery power, leave the inverter Off if we don't need AC from the batteries.  Tripp Lite suggests using 1.2 as an inefficiency multiplier:

• Begin with the AC amperes or watts of the 120V appliance. If 2.5A, then the watts are 120V x 2.5A = 300W.
• Then to determine DC amperes divide by 12V.  300W/12V = 25 DC Amperes.
• To estimate the battery Ampere-hours (Ah) required, multiply the DC Amperes x time x inefficiency.  25A x 4 hours x 1.2 =  120Ah. That’s a rough estimate and it exceeds the 50% capacity of a 200Ah battery.
• To determine amperes from an appliance using DC watts (such as a TV), simply divide the watts by 12 volts.  For example for 100 watts: 100W/12V = 8.33 A

How can I recharge my batteries? The sources of electrical energy for recharging are determined by what’s installed in your Roadtrek. These may include the following:

• Vehicle engine.
• Shore power.
• Onan generator.
• Underhood generator (GRU) - I don't have this.
• Solar panel.

How long does it take to re-charge batteries?
The more depleted the batteries, the longer the charging time required. 

• Using 120VAC and the Tripp Lite 750 Watt Power-Verter DC-to-AC Inverter/Charger, it can take 12 hours to completely recharge discharged coach batteries. This was confirmed by a factory technician. Furthermore, the charger has two settings: 10A and 45A.
• Using the Onan generator is the same as shore power because the Tripp Lite is used.
• Solar may take longer. This is determined by the amperes available from the solar panels. If a 45A Tripp Lite requires up to 12 hours, it is reasonable to assume solar may require more time because a 200W solar panel is providing about 17A. However, most RVs on solar don't draw down the batteries because during daylight hours the solar provides a part or all of the DC power requirements of the RV.

I need a 12V DC power budget.  To do this we need to do an energy audit. That’s a way to determine how far my batteries can go before I run out of DC power, and then have to recharge

1. To get maximum power available and maximize your batteries, it is better to use 12VDC appliances than 120VAC connected to the inverter because of the inverter losses. 
2. Add up the DC amperes to determine how much you use. Then calculate the Ampere hours to see how long your batteries will last before requiring a recharge.
3. Add up the ampere requirements of all of the DC appliances and things in your RV. Product labels are reliable sources. Because there are differing options, I can't provide the Amperes required for each and every device. But I do provide a list with some approximations if I know what they are:

• Lighting 12VDC (LED uses less DC energy than bulbs and fluorescent) - Varies.
• Each LED light may require 0.25A.
• Lighting 12VDC fluorescent, single 20W bulb - 1.3 to 1.8A. 
• Lighting 12VDC fluorescent, dual 20W bulbs - 1.8 to 2.2A. 
• Propane detector 12VDC about 0.1A.
• 12VDC TV (about 32W or 2.7A).
• Amplified TV antenna - varies.Macerator 17A 12VDC when running.
• Water pump (varies with pressure and flow, possibly 5A 12VDC when running).
• Inverter 2A losses or more if ON.
• Roof fan - Fantastic Fan 3350 - 2.5A when running (varies with speed).
• Bathroom fan.
• 3-way Refrigerator 12VDC for controls - approximately 1 to 2A.
• 3-way Refrigerator on 12VDC cooling - approximately 20A.
• Dometic LCD single zone thermostat.
• 16,000 BTU Suburban Propane Furnace when running - 2.8A.
• 12,000 BTU Suburban Propane water heater - 12VDC Module board - 1.0A.
• 15 inch Laptop - estimated 90 watts 120 VAC.
• Smartphone charging - estimated 5 Watts @120V,  0.5A @ 12VDC.
• CPAP machine - varies.

(c) Copyright 2019 Norman Retzke "All Rights Reserved".  See disclaimer notices.

Coach Batteries - AGM versus Lithium Ion Update

AGM Lead Acid batteries in my 210P. Mounted outside. 

Here's an update on lead acid sealed AGM batteries versus Lithium Ion (LiFePo4) as coach batteries in my Roadtrek. If you have a Chevy based Roadtrek, you probably have two 6-Volt 220Ah AGM batteries as I do.

Note: 1. I'll post an article about what we can expect from our batteries and my experience powering the stuff in my Roadtrek with AGM batteries since December 2013.

When we compare batteries, we usually look at these three types:

1. 6V type GC2 golf cart batteries. These lead-acid batteries, are not sealed, and do require addition of distilled water from time to time. They also do vent gasses.
2. 6 V type AGC2 AGM batteries. These are also lead-acid batteries, but they are sealed and require no maintenance.
3. 12V LiFePO4 Lithium-Ion batteries. These are radically different than the golf cart and AGM batteries. 

So which is the best type? That requires considering the trade-offs which depends upon your use, and how much money you are willing to spend, and warranties.  Our 210P has an Onan generator and I added limited solar too.  If we are not on shore power we need battery power to get through the night, and then we recharge. If battery power is low we can run the Onan generator, or the chassis engine. We use the inverter sparingly to give us 120VAC. So we don't need a lot of battery power. We also have propane for the stove top and for the hot water heater. Your situation might be different.

Trick question: Should one invest in LiFePo4 batteries or in Solar Panels?  I won't attempt to answer that in this post.  The answer lies in how much electrical power do you need to get through the night, when batteries are important, or use a generator.

In fact the real issue is making a useful comparison of electrical energy sources when off the grid. These include batteries, my Onan generator, and my solar panels.   This is a somewhat unequal comparison, because my Onan can provide 2,800 watts of continuous power. That's sufficient to run my Air Conditioner and the Onan consumes about 25 ounces of gasoline per hour at low power and 55 ounces per hour at full power.

My point is, we are comparing energy sources, and the costs of those sources.  This post will not compare the cost of solar panels and batteries to other sources.

Here is a quick comparison of batteries. I use Battle Born Battery as the Lithium-ion comparison because they seem to be a well made battery with a "10 year warranty".  These would also work with the TrippLite inverter charger in my Roadtrek, with a change in settings to "Gel", because according to Battle Born "the battery prefers to bulk charge at 14.4 volts and float at 13.6 volts".

1. GC2 and AGM batteries are both lead-acid batteries. One of the characteristics of these batteries is they should not be repeatedly discharged below 50% to get maximum life.  So, my 220 Ah batteries can only really provide about 110 Ah of electrical energy if I want to get maximum life from my batteries. 
2. LiFePO4 type Lithium-ion batteries are radically different technology. So they are significantly lighter in weight than any lead-acid battery of similar capacity. They can be repeatedly discharged 75 to 80% without decreasing the life of the battery. They also can tolerate more charge-discharge cycles than the lead acid batteries. A 200Ah LiFePO4 battery can provide 160 Ah of useful electrical energy. 

So why haven't we all switched to Lithium-ion batteries? It is because even if we consider the advantages, the lithium batteries also have some disadvantages.

1. LiFePO4 batteries cannot be charged if they are below freezing temperatures.
2. LiFePO4 batteries are significantly more expensive than AGM batteries.

Here are some cost comparisons. I'm going to use two different AGM batteries and compare them to a "drop-in" Lithium-Ion battery replacement made by Battle Born Battery company:

1. Amstron AP-GC2 6V AGM Deep Cycle Battery. This is rated 210 AH and is currently available for $209.99 at atbatt.com. List at $299.99. Two required to achieve 12V at list = $599.98.
2. Deka 8AGC2 (8AGC2M) 6V Deep Cycle battery. Made in USA. This is rated 220 Ah and is currently available for $389.70 via Amazon. Two required to achieve 12V = $779.40.
3. Battle Born 12V 100 Ah "drop-in" battery list $949 each. Two would provide 160 Ah of electrical energy versus 110 Ah for lead acid.  This is considering a 80% discharge versus 50%  discharge, which are the recommended maximums for these batteries. Price per battery $949 or $1,898 for two, which is required to achieve 200 Ah.  However, if you are an Escapees RV Club member, you can currently get a 15% discount.

So what are the issues? A couple of years ago, I looked at the replacement of my two 6-V AGM batteries with Lithium Ion batteries.  These were the issues I considered then:

1. Available power. The Lithium-ion batteries can provide more electrical energy and more discharge-charge cycles.  My AGM batteries can provide 110 Ah of useful electricity while Lithium-Ion which occupies the same space can provide 160 Ah. This is not trivial if one wants to boondock and could be an incentive to consider Lithium-Ion batteries.   
2. Temperature Restrictions. When I evaluated Lithium-Ion batteries a couple of years ago, I discovered that they should not be charged if the battery temperature is below freezing 32F (0 C).  My 210P carries the batteries in an outside compartment. Because we do trek when it is below freezing, that was a serious impediment. The Battle Born batteries have a low temperature charging limit of 25F.  The batteries are prevented from charging below 25F. However, they can continue to discharge until they reach a "low voltage limit" which is below 10 volts. 
3. Alternative Location. I even considered moving the Lithium-ion batteries inside of the coach as a means to get them above freezing, but that would displace useful space and add to the installation cost.
4. Cost. Comparing the Deka AGM to the Battle Born the difference is about $1,118. Comparing the Armston the difference is $1,199.96.
5. Weight. The Battle Born batteries are about one-half the weight of the AGM batteries. If weight is an issues, that reduction of about 60 lbs could be a significant factor. 
6. Warranty. Most AGM batteries can be expected to have a life of 5 years, or more. Some Lithium-Ion battery manufacturers offer a 10-year warranty. That means that one set of Lithium batteries is the equivalent of two sets of AGM batteries.  This should be considered when evaluating batteries. 
7. Temperature and voltage affects - AGM. AGM battery specifications are under "ideal" conditions. These include an ambient temperature of about 77F, discharging to no more than 50% and then immediately recharging.  That may not happen in the real world. AGM batteries do experience reduced capacity in cold weather. AGM battery life will also be reduced at higher temperatures. In other words, that 110 Ah available will decrease as the ambient temperature decreases and may be 25% less at 32F and 20 A discharge rate.  Under high discharge rates the capacity is further reduced. There is a lot of data about AGM and other lead acid batteries because there are so many manufacturers and they have been in use for many decades. 
8. Temperature and voltage affects - Lithium ion batteries. Using Battle Born Battery data for their "drop-in" 100 Ah battery, they state that the "Output voltage is flat during most of the discharge cycle". Furthermore can provide "100 Amp Continuous Current".  The company states that the batteries have low and high automatic temperature protection which shuts down the battery if temperature falls to 25F or a high temperature of 135F is reached. 
9. Lifespan. The AGMs in my Roadtrek are designed for about 1200 charge/discharge cycles if they are not discharged below 50%. According to Battle Born the lithium ion batteries "Approximately 75-80% of the battery capacity will remain after 3000 cycles in applications recharging at 0.5C or lower". The recharge "C" rating for a 200Ah battery is 0.5 x 200 A, or a charging rate of 100A. The lithium ion batteries will have much more life remaining than the AGMs after a couple of years of normal use. My AGMs should give good service for about 5 years, or longer. The Battle Born batteries will exceed that. 
10.  "Useful Life". Lead-acid batteries experience a reduction in capacity as they are charged and discharged because of internal changes, primarily sulfation. This reduction can be significant. After a year of use, my AGMs experienced about a 10% reduction. So, my useful 110 Ah decreased to about 99 Ah. Since then my batteries have leveled out, based upon voltage after a moderate period of discharge. The lithium ion batteries retain their capacity for a longer period of time. That can be important if one needs every bit of electricity available in the batteries when new. 

When I looked into replacing my AGM lead acid batteries with Lithium-ion, I also considered space requirements:

1. Inside LiFePo4. I would have to give up some under the bed space, because the Lithium Ion batteries should not be charged if below freezing. In fact, the Battle Born battery internal battery management system prevents charging below 25F.
2. Inside AGM. If I kept my two outside AGM batteries and added two inside, that would provide me with 220 AH of energy versus 160 Ah for the Lithium Ion batteries. In other words, I'd get about 38% more energy from four 6-V AGM batteries. However, those four batteries would weigh about 272 pounds. Two Battle Born batteries would weigh about 62 pounds. 
3. Inside AGM and Battle Born comparison. The above with four AGM batteries provides about 220 Ah at the best case at 272 pounds. If I added one Lithium Ion battery to total of three, that would increase the energy available to about 240 Ah. The weight would be about 93 pounds. 

The show stopper:
When I considered AGM versus Lithium-ion, I had these issues and yours might be different:

1. I wasn't willing to mount the LiFePO4 batteries inside the coach, because I didn't want to give up that space. That would be to keep the batteries above 25F while cold weather trekking. 
2. If I compare the normal life of AGMs (5 years or so) to the Battle Born LiFePo4 (10 year warranty) this changes the costs. To get 10 years of use from AGM batteries would probably require replacement after 5 years. In 10 years the two changes of AGMs is $779.40 each, for a total cost of $1,558.80 for Deka versus $1,878 for Battle Born. 
3. If I needed more overnight DC power, the Battle Born could be worth that extra $319. After all, considering the 10 year "warranty" life of the batteries, that's only about $32 per year. 

For more about Battle Born Lithium Batteries:

https://battlebornbatteries.com/





Copyright (C) 2019 Norman Retzke, "All Rights Reserved"

Original material:  https://roadtrek210.blogspot.com/

Carbon Foam Technology Batteries

Recently we had two battery choices in RVs. One was to use a lead acid battery, usually AGM and the other was to use a lithium battery, usually LiFePO4.

I've added a link to a 2015 article about these "Carbon Foam Technology" batteries at the end of this post and a link to the manufacturer's brochure. Please note that I am not endorsing this product as I do not currently own it. But it seems to be the poor man's lithium battery and I will definitely consider upgrading to it when I next change the AGMs.

Comparing benefits and trade-offs to each (AGM versus Lithium):

1. AGM batteries are relatively inexpensive, but can only provide about 700 charge-discharge cycles if operated to 80% DoD (depth of discharge).  That's perhaps four years if there is a charge-discharge cycle every other day. The cost for 220Ah batteries is about $450. 
2. Lithium batteries are relatively expensive, but can provide 2,000 cycles under similar conditions at a cost of about $1,939.

As can be seen above, the cost per discharge cycle favors the AGM batteries. To get 2,100 cycles from AGM batteries operated at 80% DoD will require three sets (exchanges) of batteries at a cost of 3 x $450 = $1,350.  That's better than the $1,939 cost of the lithium batteries.

Carbon Foam AGM Batteries
There is a different design of AGM battery available that promises longer life at 50% and 80% DoD.  This battery has been in use for about 8 years.  The Carbon Foam AGM battery is more costly than a standard AGM, but significantly less costly than a Lithium battery. Yet, it has similar performance characteristics to the LiFePO4.

Advantages and disadvantages of the Carbon Foam battery are:

1. Can be repeatedly used to 80% DoD. "Depths of Discharge to 80%-100% of rated capacity without any loss of performance."
2. Can provide 1,000 deep discharge cycles 80% DoD. That's about 1.4 times normal AGM batteries.
3. Can provide 3,600 cycles at 50% DoD. That's 3 times normal AGM batteries. (Manufacturer states life is 3,600-4,200 cycles at 50% DoD).
4. Can be stored in a partially discharged state.
5. Faster recharge (see end of this post).
6. Cost is about double that of normal AGMs. (My 220Ah cost about $490 installed). The AGM batteries currently in my coach are stated to provide 700 cycles at 80% DoD. The cost advantage of the carbon foam battery diminishes as the DoD increases.
7. Like AGMs, can be recharged at temperatures as low as (-)4F (operating range is -4F to +131F).

Technology
According to the manufacturer, here is what is different about the Firefly Oasis AGM battery:  "The Oasis uses a patented microcellular carbon foam grid imbedded [sic] onto the internal negative plates. This grid prevents large sulfate crystals from forming, thus the sulfate will easily dissolve back into the electrolyte with a full charge. For a full capacity recovery, no “equalization” is required with Oasis. Only do a full recharge as needed to “open up” the full capacity once again. There is no permanent damage or capacity loss from extended PSOC (partial state of charge) operation, or from deep discharging to a low SOC (state of charge)."


Link to 2015 Article:

https://www.practical-sailor.com/blog/Can-Carbon-Foam-Batteries-Meet-Hype-11694-1.html


Recharging
"The Firefly showed to have charged at a faster rate than a smaller capacity AGM battery. That, coupled with the fact that there is no need for it to be fully recharged each cycle, makes the Firefly Oasis Gp31 the closest thing to Lithium in charging performance, and has established itself as the gold standard of Lead Acid AGM batteries."

Link to the recharging comparison article:

https://coastalclimatecontrol.com/index.php/blog/186-firefly-batteries-new-testing-reveals.html


Manufacturer's Brochure
Link to a pdf of the brochure:

http://fireflyenergy.com/wp-content/uploads/2017/08/12VG31-brochure-SPI-LV-1.pdf

Original material:  https://roadtrek210.blogspot.com/

AGM Batteries, Separator Operation, Charging and Voltmeter

Replacement Battery Separator

December 2019:
I installed a replacement battery separator and it works differently from the old one. See Note 5 in the Battery Separator section, below.

September 26, 2019:
After I installed the digital voltmeter I was able to more closely monitor the coach battery voltage as well as the operation of the separator. Earlier this year I purchased a replacement separator as a "spare".  The old separator seems to work inconsistently or intermittently. For example with the engine running and a 14V chassis battery voltage the separator will connect the chassis and coach batteries. But sometimes it does not!  Go figure. I've decided to install the spare and I'll provide an update after I do.

October 6:  I added information on "clicking" battery separators. This has been reported by owners.
To go to the section on the battery separator, click here: Click here to go to the post section about the battery separator.

June 26, 2019 added the SOC table for the AGM batteries in my 210P. Note, I replaced those batteries and the table for your batteries may differ.

July 3, 2019 clarified separator main and aux connections.
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Read the notes at the end before proceeding! This post is not a recommendation that owners perform their own electrical service. Working with electricity can be dangerous and can result in personal injury, or death or damage to your Roadtrek. 
Sorry if I created a scare, but one does have to be careful if tinkering with electrical systems. Mistakes can be very costly, or can result in personal injury.

My 2013 Roadtrek 210P has:

• 2 x 6 volt AGM coach batteries, about 220Ah
• Tripplite 750W Charger/inverter
• Battery Separator (bidirectional)
• LED 12V display (four round indicators)
• Digital 12V display (added by me)
• Onan generator (2800 watt)
• 50 watt solar panel, for charging the coach batteries (added by me)

2013 Roadtrek 210P display/switch panel
This is the display/switch panel on my 210P. In the photo the Onan generator is running and supplying 120VAC power. The Battery Disconnect is ON and this is indicated by the Battery On blue indicator. As a consequence the batteries are charging:

Charging the coach batteries
It is possible to charge the coach batteries:

• While on 120V "shore power"  and using the Tripplite
• While running the vehicle engine (see the Battery Separator section for limitations)
• By running the Onan generator and using the Tripplite.
• On solar

The limitations of the battery LED indicator

The LED indicator of the Roadtrek is a voltmeter which is somewhat limited. It indicates these battery conditions while the soft BATT button is pressed:

• L - Low
• F- Fair
• G- Good
• C- Charging

Note that the "C" indicator may be on even when the battery is discharging. This may occur shortly after disconnecting the coach from AC or stopping the vehicle engine. The reason is because the coach battery voltage is higher than normal 100% charge. This is what is called a battery "surface charge" and after a few minutes with a small DC load such as the slowly running roof fan, this charge will be dissipated and the true condition of the battery will be indicated. 

In the photo the Battery Disconnect switch BATT is ON as indicated by the illuminated "Battery ON" light. Pressing the Battery button displays the battery situation. The highest (rightmost) illuminated indicator displays the condition, which in the photo is a C for Charging:

Using a Voltmeter to Monitor the Battery Voltage
Monitoring the coach battery voltage is helpful for determining battery capacity. We may want to know how much energy is available in our coach batteries. A voltmeter is useful for doing this.

My Roadtrek didn't have a voltmeter, and the power/switch/display area isn't set up for one. However, there is a 12V "cigarette lighter" style receptacle in the rear overhead compartment, above the DVD player. Unplugging my powered antenna allows me to plug in a voltmeter to check the battery voltage:

12V receptacle

Here's a typical digital plug-in voltmeter. These can be purchased for as little as $7:

Plug-in Digital Voltmeter

What does that voltmeter display mean?
Here's a typical chart for AGM batteries. If we are aware of the voltage at the batteries, we have a rough idea of the "capacity" remaining. For example, if your voltmeter displays 12.50 volts, then you have used about 20% of the capacity or available energy in your batteries. However, I must note that it is not recommended to fully discharge batteries to 0%. That will ruin them.

You will have to decide how low you want to run your batteries. For longest life under moderate temperatures (77F is ideal) some recommend not dropping below 50%, or  about 12.05V.  Dropping to 20% (80% discharge) reduces battery life, but provides energy for a longer time. That's discharging to about 11.66V. Going lower will severely reduce battery life. Fully discharging AGM batteries can damage and ruin them. What does repeatedly discharge below 20% mean? It means severely reducing battery capacity, to the point the batteries cannot provide energy when disconnected from the Tripplite charger (when charging the battery).

Note that you might have poor batteries and be unaware. The 750W Tripplite inverter/charger can provide up to 45A (amperes) of charging current when on shore power. That's about 540 Watts. The Tripplite can not only charge batteries, but also power 12V DC appliances including lights, fan, propane furnace and so on when the Roadtrek is connected to shore power, even with poor batteries.

Having a voltmeter helps to determine just how long your batteries can support your RV when you are disconnected from AC power. For example, suppose you are running your fan, there are interior lights on, the occasional water pump, and your 3-way refrigerator is on propane (some 12V is used). After three hours the voltmeter indicates 12.5V. That means it took 3 hours to use about 20% of your battery capacity. Another 3 hours will use an additional 20% or more. That implies you'll have enough battery power to make it through the night (lights off, pump off and fan on).

This table is typical. Your AGM batteries may vary somewhat.

Typical AGM Battery Table

I replaced my AGM batteries and this is the SOC table provided by the manufacturer.  Your batteries may differ:

What does "reducing battery life" really mean?
AGM and gel lead-acid batteries are chemical devices. They generate electricity using lead plates or mats and an acid liquid. As we repeatedly discharge these batteries, certain deposits form inside them that reduces the capacity. Capacity is the ability to deliver full current for a certain amount of time before the voltage decreases below a useable level. As batteries age, that ability diminishes. For example, a new, fully charged battery can provide a specific amount of current for a specific length of time. Think of this as ability to run your fan, lights, DC for a propane refrigerator and a laptop. With new batteries, you might be able to do that all night. As the batteries age, the length of time decreases and you will find the batteries can no longer do so. And the lights will go out before dawn, whereas before they could be left on all night.

Alternative Voltmeter
I decided to add a digital voltmeter/ammeter. The advantage is I can monitor the amount of current being used and the digital meter provides me with a better idea of the "state of charge" and how much electrical energy might be available. The higher the current, the faster I will drain the batteries. The meter includes a Watt hour counter ("energy"), so I can roughly monitor how much energy is used overnight, should I choose to do so. The meter includes both high and low voltage alarms. This is detailed in another post:

The following data is according to the Tripplite 932768 manual for  750 Watt "PowerVerter DC-to-AC Inverter/Chargers", the Tripplite data sheet and a Roadtrek Manual

Charging the AGM batteries
The batteries can be charged from 120VAC. This is either via shore power or by running my Onan generator. One thing to keep in mind is to turn ON the battery disconnect switch before plugging the RV into AC power or starting the Onan generator. That is per Roadtrek recommendations for my RV.

How long can it take? If the batteries are depleted, it can take 12 hours or longer to fully charge the batteries.

Are there circumstances under which I can't charge the batteries? If  the battery voltage decreases to below 10.0V (+/- 3%, or somewhere between 9.7 and 10.3 volts) a low voltage cutoff will occur. The Tripplite inverter/charger will not charge the batteries if the battery terminal voltages fall that low.   If your vehicle engine is running, the battery may be charged via the standard alternator, if the battery separator allows (see the Battery Separator comments below). A underhood battery separator isolates the chassis battery from the coach batteries when the engine is not running.  However, batteries below 10.5 volts should be checked. They could be damaged.

How can I determine the state of charge? The Tripplite charger/inverter includes a display. However, it cannot be viewed without removing a cover.  Here is a photo with the cover removed. The Tripplite has two rows of LED indicators. One blinks green when on 120VAC and the Inverter switch is "OFF". Otherwise if on 120VAC and the Inverter switch is "ON" then it will be steady green. The switch is located on the Roadtrek display/switch panel near the side entry door. (see the first photo in this post, above).

The other Tripplite indicator goes from off to red to yellow to green depending upon the state of charge of the coach batteries. If charged more than 91% and on AC, one will be blinking green (on AC and inverter off) and the other will be steady green (91% or better charge).

The Tripplite is located in an interior compartment to the left and in front of the powered sofa when you are facing the rear of the RT. The Trippite has a fan and at times you will hear it running. However, there are exposed connectors/wiring so you do need to be careful. If you have any concerns, get a pro to do this.  DO NOT TOUCH ANYTHING.  After you have a pro demonstrate this to you, you can decide if you want to do it yourself in the future.

To reveal the Tripplite, lift up on the top wooden cover at the front and then slide it forward.

Tripplite and DC Electrical Compartment

The next photo is a close-up of the indicators on the Tripplite. The arrow points to a flashing green LED. That means the Tripplite is on AC with inverter OFF. The other indicator which is below the blue cable is the charging indicator. In the photo the bottom LED is green which according to the Tripplite manual indicates "battery capacity charging/discharging 91% - Full"

Here's the table from the Tripplite manual. There are a number of switches for configuring the Tripplite. These LEDs function with Switch in "AUTO/REMOTE" or “Charge  Only” Position. That is how my Roadtrek was delivered.

Approximate Battery Charge Level while charging and discharging (bottom indicator in the photo below):

• Green = 91% to Full Capacity (see the Tip below)
• Green and Yellow = 81%-90%
• Yellow = 61%-80%
• Yellow and Red = 41%-60%
• Red = 21% to 40%
• All three LEDs off = 1% to 20%
• Flashing Red = 0% (Inverter shutdown)

Tip: How can we determine the Battery Charge Level above 91%?  At about 91% the AC power of the Tripplite is about 10 amperes. At about 100% charge it will decrease to 2 to 4 amperes, assuming the inverter function is OFF. Monitoring the AC current consumption of the Tripplite can aid us in determining the battery charge level above 91%. I have a Progressive Industries EMS on my 210P and I can monitor the AC current consumption. If you have a similar arrangement, so can you. However, you do have to avoid running anything else in the coach to get a reliable reading from the AC draw of the coach.

Tripplite Fault Conditions (bottom indicator in the photo below):

• All three flashing slowly (1/2 second on, 1/2 second off) = Excessive discharge (inverter shutdown)
• All three flashing quickly (1/4 second on, 1/4 second off) = Overcharge (Charger shutdown)

The arrow in the photo points to the 120v power "Line green LED":

• Steady Green = Roadtrek inverter switch "ON" and the coach is on AC power (shore power or Onan generator)
• Flashing Green = Roadtrek inverter switch "OFF"
• Yellow = Roadtrek inverter switch "ON" and Coach battery providing power to 120V receptacles via the inverter.
• Red = Roadtrek inverter switch "ON" and power demanded of the inverter exceeds 100% load capacity

Tripplite LED Indicators

Tripplite Operation and Inverter Selector
The Tripplite has a 3-way slide switch for selecting the "Operating Mode". See the photo below:

Left Position - Auto/Remote
Center Position - DC OFF
Right Position - Charge Only

The "Auto Remote" position ensures that the connected equipment receives constant, uninterrupted AC power. It also permits the Inverter/Charger to be remotely monitored and controlled (in my 210P the Roadtrek inverter switch turns on and off the "inverter" operation if the Tripp-Lite slide switch is in this position).

The "DC OFF" position de-energizes the unit and connects AC OUT to AC IN. In my 210P this slide switch position disables the Roadtrek inverter selector.

The "CHARGE ONLY" setting allows the Tripplite to charge the batteries faster by turning off the inverter, which halts battery discharging.

Operation Switch in DC OFF position

Battery Separator.

Battery Separator - Bidirectional
The battery separator is under the vehicle hood. It controls the connection of the vehicle battery and the coach batteries. In my 210P the battery separator is a "bidirectional" 200A module with a relay for 12V systems. You may have a "unidirectional" model and if so, your battery separator operates differently than the following; for a unidirectional separator see the description in the next section.

The [bidirectional] separator monitors the engine ("Main") and coach ("Aux") batteries. The manual states "If either battery bank is above the connect threshold [13.2V], the relay [closes and] connects the two banks together. If either battery is below the disconnect threshold [12.8V] the unit will open the relay." However, once connected both batteries are at the same voltage. Opening the relay disconnects the engine and coach batteries, preventing the draining of both.  "The connect threshold is set to a nominal voltage of 13.2V, which would only be reached when the charging system is operating. The disconnect voltage is set to a nominal 12.8V, which is near the full charge resting voltage of the batteries. " 

I've monitored the separator and it seems to be intermittent. At times, if the coach battery voltage is less than 12.8V the engine battery will not charge the coach batteries because the separator disconnects if either battery bank is below that voltage. When this occurs, the battery must be charged via 120VAC (shore power or Onan generator). Or via solar. In other words, the battery separator in my Roadtrek doesn't seem to consistently connect my vehicle alternator to the coach battery if the engine battery is 14V and the coach battery is less than 12.8V. That's a coach battery that is 90% charged. See note 7.

According to the separator manufacturer:  The connect threshold is set to a nominal voltage of 13.2V, which would only be reached when the charging system is operating. This will cause the relay to close and the charging system can charge both banks of batteries. The disconnect voltage is set to a nominal 12.8V, which is near the full charge resting voltage of the batteries. This will cause the relay to be opened shortly after the engine is stopped, attempting to preserve 100% of the starting battery capacity for engine cranking."

Note 1: In my Roadtrek the terminal labelled "Aux" is connected to the coach batteries. The terminal labelled "Main" is connected to the chassis battery:

Note 2: The vehicle alternator (Main)  will connect to the coach batteries (Aux) if either the vehicle or coach batteries are above the "connect" threshold of about 13.2V, which is 100% charge. After connecting the batteries will remain connected unless one of the batteries falls below 12.8V. This was confirmed with a new battery separator. See Note 5.

Note 3 :  The separator includes a momentary "auxiliary start function".  The start terminal must see at least 3V* to activate. The auxiliary [coach] battery must read at least 10V*." "This is the input for engine start signal override. When power is applied to this input, the relay will close if the Aux. Battery [coach] is no less than 0.85 Volts below the Main battery [chassis]."  In my Roadtrek this is not used.

Note 4:  According to the separator manufacturer, "* = Typical voltage settings have a +/- 2% tolerance".

Note 5:  Update December 2019. I replaced the battery separator and the operation of the new one is different than the old one.  If either the coach or engine battery is above the "connect" voltage threshold of about 13.2 volts  then the separator connects both coach and engine batteries.  I've monitored this for several weeks and the operation is consistent. If the engine is running the engine battery voltage is about 14.0 volts and the separator connects the engine battery to the chassis battery. If the engine is not running and I connect the Roadtrek to shore power, the Tripplite charge voltage rises to above 13.4 V and the chassis batteries and Tripplite are connected to the engine battery. This is not the way the old separator operated and I can only assume that the old separator had a flaw or failure.

Separator Options
The separator includes some options, including a "start signal" but that is not wired on my Roadtrek. The "start signal input" is the input for engine start signal override. When power is applied to this input, the relay will close if the Aux. [coach] Battery is no less than 0.85 Volts below the Main [chassis] battery.


Where is the Separator located?
The battery separator is the device in the center of this photo with the two red rubber boots. In my Roadtrek the terminal on the right is labelled "Aux" and is connected to the coach batteries. The terminal on the left is labelled "Main" and is connected to the chassis battery:

Alternate Battery Separator - "Unidirectional" Type
The battery separator is under the vehicle hood, see the photo above. It controls the connection between the vehicle battery and the coach batteries. In my 210P the battery separator is a "bidirectional" 200A module with a relay for 12V systems.  The following is the description of a "unidirectional" model. These two models operate differently. You need to determine which you have in your RV.

The unidirectional separator is a 200A battery separator modules with an integrated relay for 12V systems. The separator monitors the engine and coach batteries. If the Main battery is above the connect threshold, the relay connects the two battery banks together. If the Main battery is below the disconnect threshold the separator will open the relay. You will have to determine which battery bank, Chassis or Coach is connected to the "Main" terminal.

The connect threshold is set to a nominal voltage of 13.2V, which would only be reached when the vehicle charging system is operating. This will cause the relay to close and the engine charging system can charge both the engine and coach batteries. The disconnect voltage is set to a nominal 12.8V, which is near the full charge resting voltage of the batteries. This will cause the relay to be opened shortly after the engine is stopped, attempting to preserve 100% of the starting battery capacity for engine cranking.

Battery Separator - Bidirectional - "Clicking"
The battery separator is under the vehicle hood, see the photo above.  From time to time, you might hear a "clicking" sound if your hood is open. That could be the relay of the separator opening or closing.

For a bidirectional separator the relay will close as noted above if the vehicle battery/alternator is above 13.2V and the coach batteries are above 12.8V. Or vice-versa. If either of these falls below 12.8V the relay will open. When the relay closes it connects the vehicle battery/alternator to the coach batteries and when it opens it disconnects or separates these batteries.

The bidirectional will connect the vehicle and coach battery systems if the coach rises about 13.2V and the vehicle is above 12.8V.

At rest, my vehicle battery is about 12.6V. Fully charged my coach batteries are about 13.2 volts after dissipating the "surface charge".

If one has a solar charging system for the coach batteries, it would be possible for intermittent connection of the two systems if the solar system rises above 13.2V and the engine battery is above 12.8V.  Depending upon load and sunlight conditions, if the coach battery falls below 12.8V or about 90%, then the separator relay will open, disconnecting the vehicle and coach batteries. If the sun comes out, or solar improves and the coach battery terminal voltage increases to above 13.2V (which will happen while charging) then the separator relay will close, connecting the two battery systems.  As the coach battery discharges, the terminal voltage will decrease. When sunlight increases, then the separator will again close the relay, "click" and the two battery systems will be connected.

Of course, a faulty separator may also close the relay at unexpected moments.

Solar.

Solar:
In 2014 I  added a 50-watt solar panel and a desulfating solar controller.  Using a 50-watt solar panel provides a maximum 4.17 amperes of charging current at 12V during peak sunlight conditions. That's more than sufficient for maintaining or topping off the batteries.

Notes:

1. This post is not a recommendation that owners perform their own electrical service. Working with electricity can be dangerous and can result in personal injury, or death or damage to your Roadtrek. 
2. This information is provided "As Is" and no warranty or claim of accuracy is given. Your Roadtrek and its equipment may be very different than what is portrayed here. 
3. Refer to the Roadtrek owners manual and the Tripplite Owner's Manual for complete information. 
4. The Tripplite inverter/charge includes 120V surge protection. In other words, outlets that are powered by the "invert" mode will have surge protection. Any others in the coach will not have any surge protection unless it is added. In my case, I have an electrical management system (EMS) on the shore power line. I don't have such a thing on the generator power output. 
5. For troubleshooting of the Tripplite, refer to the owners manual. 
6. This post is based on several other posts in this blog as well as recent social media posts by me. I'm providing this so I won't have to write this up again. 
7. My coach batteries exhibited difficulty at about 3 years. I suspect the problem was the model battery separator Roadtrek installed in my 210P. The separator won't connect the vehicle alternator to the coach batteries unless the coach batteries are at 100% charge. 
8. All info on the battery separator is per the manufacturer's data sheet.