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/

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. 

Lithium Batteries and Solar Power, Revisited

Winter approaches and we are near the end of our first two years with a camper van. It is time to winterize and to review my "to do" list. One item has been improving the coach battery system. We did store the camper for two winters with the batteries on a solar panel.

This worked fairly well. But, I wasn't happy with the amount of power provided by these 220Ah batteries, and began exploring alternatives in late 2013, immediately on purchase. I'd done the numbers and knew we would be on the edge based upon our intended use of the vehicle. Why do I say "on the edge?" It is because of the available capacity of these batteries, which is not 220Ah if one wants them to have a reasonable life expectancy of 5 or more years.

A Short Review
What is the true available 12VDC power? 220Ah of AGM batteries can only provide 110Ah while keeping them above a "safe" discharge level of 50%.  What does that mean? If one wants to run some appliances and an inverter, the batteries can provide the following power:

• 5 amperes (60 watts @ 12 volts) for 22 hours, or 
• 6.5 amperes (78 watts @ 12 volts) for 16 hours, or 
• 8.5 amperes (102 watts @ 12 volts) for 12 hours, or 
• 12 amperes (144 watts @ 12 volts) for 8 hours. 

The real issue is having sufficient battery capacity to run necessities through the night while off shore power and without a generator. At a minimum this would be the refrigerator and a vent fan or the furnace plus some lighting. The loads of your rig might be different than mine. To run any 120V appliances including a PC would require the inverter which has losses as part of the process of converting 12VDC to 120VAC. It would be best to use 12VDC appliances and a PC which can run from 12VDC. We've got a propane range top and so we can use that for cooking. If the weather is mild, it is possible to use the propane BBQ or if allowed, a wood burning campfire. These things reduce the electrical requirements for the batteries. Of course, we can simply fire up the generator. However it is my desire to make it through a typical night in mild (40F to 85F) weather without shore power or running the generator. That is not necessarily a daily requirement. In fact, based on our actual experience. we only need overnight battery capacity on an occasional basis. That translates into the cost-benefit analysis of the battery and solar system.

The existing AGM batteries, if in excellent condition could provide about 6.5 amperes for 16 hours. I do need to emphasize that I am assuming the batteries are in good condition and fully charged. If not, then less power would be available. Why 16 hours? That's maximum for winter with darkness and operating on batteries from 5pm to 9am. I'm assuming cool temperatures in which there would be no need for supplemental coach heat beyond use of the furnace. However, I've done some analysis of our electric blanket and that is a viable alternative.

If my refrigerator operates on propane I do need some 12VDC for the controls. The furnace electronics and fan also require 12VDC. Lighting loads vary. I've got fluorescent and LEDs. In a pinch we could use hockey puck LED lights which run of AA batteries. But we don't want our "tiny home on wheels" to morph into "our tiny cave on wheels."

How Much DC Power is Used?

• Suburban Furnace = 2.8A (intermittent)
• Max-Air Fan @ Medium Speed = 1.5A
• Refrigerator 12V electronics = estimated 1A
• Propane/CO Alarm = 0.1A
• Smoke Alarm = 0A (9V battery)

These  items consume 5.4 amperes. That is approaching the maximum 16 hour capacity of the batteries, and based upon experience that's a realistic maximum for daily hours with less than perfect batteries. It would seem that Roadtrek did a good job sizing this system. Remember that the furnace runs intermittently. That's why I didn't include the lighting load. However, if one uses the inverter, then the requirements increase by about 1.5 amperes or more. That's because of the inefficiency and losses in the inverter.

Do I Need Lithium Batteries?
Based upon our actual experience since December 2013, I would say that we do not. It is true that our current battery system is marginal. However, based upon actual needs, we don't need to do an upgrade at this time.

That said, it is possible I will replace the AGMs with LiFePO4 batteries when that time comes. Here is my reality: It is all about cost-benefit analysis. I do have a design and it will be easy to adjust the design as time goes on. With each design modification I'll get current prices and current technology.  Trigger events to upgrade would include battery failure, inverter/charger failure, a desire for more solar than I currently have, and so on.

It is also possible that some day I may take this on as a "hobby" project. But I am under no pressure to make the modifications at this time.

Here are some links to earlier posts on this subject:

http://roadtrek210.blogspot.com/2015/02/agm-battery-alternatives.html

http://roadtrek210.blogspot.com/2015/02/are-lithium-coach-batteries-expensive.html

Here is a handy calculator to help you determine how long your coach batteries can handle a specific load in amperes:

http://www.batterystuff.com/kb/tools/calculator-sizing-a-battery-to-a-load.html

Note: Edited amps used to add CO/Propane detector, misc.

Are Lithium RV Coach Batteries Expensive?

Here's a bottom line for a small RV system, using off the shelf lithium battery components. I'm editing this post to add the following which I think is a very important consideration:

AGM batteries 220Ah = 110Ah useable,
Lithium (LiFePO4) 200Ah = 160Ah useable,

In other words, 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. Now do I have your attention?

What I am planning is not a "build it in your basement" system comprised of battery packs assembled at home from hundreds of batteries. There are some serious considerations when using lithium batteries, which can be safe and environmentally superior to lead acid batteries. Those batteries do require monitoring and controls so that a cell failure can be managed. My concept system which will probably be built is comprised of pre-assembled batteries packs and off the shelf controllers and solar panels. This system is similar in design to current AGM coach battery systems:

Battery watts: 1200 (or 2400) (1.2-2.6 kWhr, replace 2-6V 220Ah AGM batteries)
Solar Panel = 140 Watts
Cycles: 2000 to 3000 at 70-80% discharge (DoD). Up to 5000 cycles possible. (See notes).
Self discharge = less than 3% per month.
Battery weight = 25 to 33 lbs.
Battery storage temperature limits = -20 to 114F
Battery operational temperature limits = 32 to 114F (some batteries are rated 5F to 115F).
Includes MPTT Solar Controller and 140 watt solar panel.
Includes 120V charger for lithium batteries.
Cost of entire system components: $1,690 - $2,600

Why the cost differences above? There are different technologies available. The most reliable are the most expensive. I think the lower number is realistic. After all, I won't be sailing my RV around Cape Horn. Note: Read the notes at the conclusion of this post for some important info that impact the specifications above.

Can I Get More Power?
The above can be "scaled up" with more batteries, larger solar panels, etc.  A 2400 watt (whr) system could cost about $3,000. The batteries would weigh about 60-65 lbs, which is about half of a similar AGM battery. The costs are for components, but excludes installation and tax.

A 4800 watt system could cost about $5,600.  As you can see, at the higher wattage the cost is approaching about $1 per watt. However, it is possible to get batteries for as low as $0.55 per watt.

Quick Comparison - AGM Limitations versus Lithium
It's useful to keep in mind that the list price of an additional 2400 watts of AGM batteries in a Roadtrek 210P is currently $871. The battery cost difference is why lithium is not currently standard. In recent years there have been some real price drops in lithium and today, 2400 watts of AGM batteries cost about $500-600 while similar lithium batteries begin at about $1,800.

However, AGM batteries are temperamental. They have longer charge times, can and do sulfate, weigh twice what lithium batteries do. AGM batteries perform longest with a 50% discharge (50% DoD, or Depth of Discharge). In other words, a lithium battery with an 80% DoD limit can provide 30% more power each and every day as compared to an AGM battery. Such a lithium battery is designed for at least 2000 cycles, which is about 7 times the life of an AGM battery. Achieving 5000 cycles would result in a system which could have a life measured in decades.

Of course, any RV manufacturer's pricing includes mounting and wiring systems as well as installation labor, etc. I am convinced I could install an entire system, including improved solar and MPTT charging system with at least 2400 watts (whr) of lithium power for a cost of about $3,000. If I want to get wild, I could go for 4800 watts at about $6,000.  The 2400 watt system would be almost a "drop in" solution. 3600 or more watts would require a closer look at the available battery space.

Other Battery Considerations
One more thing to consider is cycles. That's the number of times a battery can be charged and discharged. A Deep Cycle AGM battery, if discharged to not less than 60% the cycle life will be 300 plus cycles. (That's per reputable battery sources). An AGM battery might achieve 500 cycles. A lithium battery is good for 2000 to 3000 cycles at 80% DoD and ideal temperatures (see the notes). In other words, a lithium battery system is rated for a lifespan 6 to  10 times longer than that of an AGM battery system.  That is one of the reasons manufacturers are beginning to look seriously at replacing AGM battery systems with lithium battery systems.

What's the Limit?
Most costly component is the batteries. To get to 20,000 watts as Roadtrek is experimenting could require about $10,000-$12,000 in batteries (at wholesale). I would guess those batteries weigh about 500 lbs. However, to put this into perspective a Roadtrek 210P comes "stock" with two AGM batteries rated a total of 2400 watts. 4800 watts with AGM batteries weighs in at about 280 lbs.

What does 20,000 watts of AGM batteries weigh?
I'd guess that 20kW (kWh) of AGM batteries would weigh in at about 1,200 lbs plus the weight of the system to contain them. Similar capacity lithium batteries would weigh about 500 lbs. However, there are differing lithium battery technologies available, and that influences both volume taken by the batteries and weight. (See note 10).

Why would I do this? 
Well, I think I'll be replacing my AGM batteries next year, less than 36 months after vehicle purchase. Replacement with similar batteries will cost me about $600. In other words, the battery cost has been about $300 per year. Add to that the following possibilities achievable with an upgrade:

• zero maintenance with solar (I do have solar on the AGM batteries)
• no lead
• 10 year life (okay, let's assume 6 years at 75% real, available power).
• 80% depth of discharge
• A real 1920 watt-hour available rather than pretend 2400 which is at best 1200.
• I'd like to get more electrical power when off the grid than I do currently, and I'd like to achieve this without running the engine, or starting the generator. I'd also like to have more power available for cooking when off the grid and conserve propane. I have no intention of living on solar power.  The existing system is rated about 1.3kWh and I think I can double that with the lithium batteries. 
• No need to charge below freezing during vehicle storage. It's my understanding that lithium (LiFePO4) batteries should not be charged if they are below freezing. However, they can be stored for long periods under freezing conditions and can discharge okay in cold weather. (Note 11).

Notes:

1.  I have the advantage of being able to prototype and test such systems. I think a "drop-in" upgrade package for RVs would be useful.
2. I'm currently most interested in LiFePO4/LiFeMnPO4 battery technology. I want batteries which are safe.
3. Costs are determined by battery technology.
4. Battery prices are all over the map. Lowest cost is about $0.55 per watt (whr).
5. Battery life for AGM lead-acid and lithium (LiFePO4) batteries are determined under somewhat ideal conditions. Those conditions include ideal DoD as well as ideal ambient temperatures. Battery life is reduced under higher temperatures. What's ideal? Depending upon the battery, 74-77F is ideal.
6. In the real world some RVers are attempting to live off solar systems with lots of solar panels and large battery systems. This requires sunshine.  Unfortunately, many such sunny areas also get higher ambient temperatures and that's not good for batteries. Over in Tucson they talk about five annual seasons, of which one is named "fire." Elevated temperatures reduce battery life. So what's reasonable? I'm going to assume a 25% reduction in battery capacity within 5 years. However, for a  lithium (LiFePO4) battery that would be far superior to my AGM batteries.
7. A lot of what we know, and what we are doing, is based upon lead acid battery technology. For example, with AGM batteries it is preferred to keep them fully charged. So this approach was also applied to lithium batteries. However, there is now a concern that maintaining lithium batteries at full charge may actually reduce their usable life. In other words, there may be a trade-off and that has fueled some argument about what is the best way to maintain lithium batteries while achieving the longest possible life.
8. I am concerned about the above. A lot of what we currently know is based upon old lead-acid theory and requires years to validate in the "real world." When one is spending $thousands on batteries, that should be a concern. Roadtrek currently has a prototype with 20kW (kwhr?) of lithium batteries. Will they get it right?
9. Why do this? I'll post on that later, but I've provided a brief explanation in the text of this post.
10. You may wonder about that 20kW number. That's what a Roadtrek blog has stated a prototype lithium system has. I assume they meant a capacity of 20kWh (20 kilowatt hours). Not beyond the realm of possibility. I've seen a similar battery pack and it measures about 25 inches x 24 inches x 15 inches and weighs in at about 425 lbs.
11. It's my understanding that it's okay to discharge these batteries if the temperature is below freezing and they can be stored for long periods below freezing. However, they should not be charged if the temperature is below freezing. This will require some additional research on my part. 

Oops, I am so used to working in higher power systems I typed "kW" in several places when I should have typed "W." I have corrected this and now indicate "watts" where that is so. I also omitted the 120V charger for the lithium batteries on my list. It was included in the costs. It may not be clear from this post, but I could achieve an increase in available kW with the lithium batteries. My current 6V batteries are rated 220Ah under "ideal conditions."