Comparing AGM and Lithium RV Battery Systems

Comment added August 10, 2017; see the notes at the bottom of this post, in particular #5.

A couple of years ago, I considered swapping my AGM batteries for Lithium (LiFePO4). I looked again in January 2017 and I again decided against doing that.

What's the problem? It's simply dollars and sense.

As can be seen above, running both 200AH lithium and AGM battery systems to 80% depth of discharge (DoD) the cost of the AGMs is sufficiently less. So, while the lithium batteries are more "elegant" from an engineering perspective they may not provide more benefits and at a higher cost. Read on for the details.

Here's the background:

Battery life: Lithium 2000 cycles at 80% DoD. AGM 700 cycles at 80% DoD.

Cost for 200 AH: Lithium with BMS = $1,939. AGM = $450.

As can be seen above, here is the arithmetic:

AGM: 2100 cycles at 80% DoD requires (3) sets of batteries, or 3 x $450 = $1,350.
Lithium: 2000 cycles at 80% DoD requires (1) set of batteries at $1,939.

Conclusion: use AGM batteries, install a better battery monitor and run the batteries to 80% DoD. Compared to Lithium, save $589 while getting about the same performance and none of the low temperature headaches.

Other Considerations: 

1. AGMs weigh more than LiFEPO4 batteries, so if I needed more than 200AH of battery capacity (more than 10 hours @ 16.8A) then I should re-evaluate an alternative to the 200AH of AGMs I have. 
2. Installing lithium ion batteries will also require additional electronics, including a charger and an Energy Management System, at additional cost.  My AGM system includes the necessary electronics, I added a digital Volt/Ammeter, so all I have to do is replace the batteries at the required time.
3. AGM batteries can be charged at below 32F. LiFEPO4 batteries have to be heated to be charged at 32F and below. In my case (AGM), that means no heaters and no wasted electrical energy warming up lithium ion batteries prior to charging. In my case, that makes installations simpler. I can keep the 200AH of AGM batteries in the outside compartment. I had decided that if I chose lithium ion batteries that I would install them inside the coach. I would have had to give up valuable real estate (square footage) to do that. 
4. Because Lithium ion batteries weigh less than AGM batteries, if I really needed 400AH or so, I'd look at the volume and weight differences. But that is not currently an issue for me. 
5. Over on social media, putting info about the relative merits of AGM batteries versus Lithium (LiFePO4) usually causes a bit of a stir. Here is my response to one social media rebuttal:  "I agree about the "light duty", but that also changes the cycles for AGMs and what' the point of buying a lot of capacity not to use it? What is missing in the chart you provided is remaining capacity and that does make a difference. The charts for the AGMs I'm using indicate about 60% capacity remaining after 80% DoD and 700 cycles. It is a known AGM characteristic that capacity does gradually decline, and by 700 cycles capacity decrease to 50-60% is usual. That certainly can have an impact on [battery] selection. Specifics may vary from manufacture to manufacturer. I used the table of the AGM battery manufacturer in my coach, and it might be accurate or not. I also based cost on the actual cost of the batteries (AGM's in my coach and the current price of the LiFePO4's I was considering). The lithiums don't include installation, which would definitely not be drop in. One other issue to beware of in AGMs is full discharge. The battery numbers vary based upon "relative" DoD. In other words, some battery specs go all the way down to 10.5 volts, which is a dead AGM battery. Other charts use relative terms in which the 0% AGM charge is 11.66V or so, which is actually about 20% DoD. Everything I've seen indicates that AGMs when fully charged generally have about 80-100% capacity which gradually diminishes. Lithium batteries also experience capacity loss, although that doesn't seem to become significant (below 80%) until about 400- 500 cycles. I'm sure there are installers who have better data based upon dozens or hundreds of installations. On the other hand, they might not want to provide data that kills the golden goose.

New Voltmeter-Ammeter-Wattmeter for AGM batteries - Part 2

New Ammeter-Voltmeter-Wattmeter

September 15, 2017: Added short video clip

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Short video:

New Ammeter-Voltmeter-Wattmeter

See Part 1 for the background information about the AGM batteries in my roadtrek 210P:

http://roadtrek210.blogspot.com/2017/08/new-voltmeter-ammeter-wattmeter-for-agm.html

Why add a digital voltmeter-ammeter?
The decision to add a digital meter was easy. Then I proceeded to decide upon the type of meter. I had seen a FMCA Roadtrek Chapter Cyberrally post about how someone added a digital meter and I wanted to do the same.

Finding a meter wasn't all that difficult. A meter which stored "Ampere Hours" would have been ideal, but I opted for a digital voltmeter-ammeter-wattmeter. The selected meter also included adjustable alarm points for high and low voltage. That would be useful for monitoring low battery voltage, or a point at which I wanted to pay closer attention to battery draw.

I ordered the meter ($15.99 at the time) with DC shunt. I wanted to connect it directly to the battery so I could monitor battery voltage even with the battery disconnect "off". A switch and protective fuse was necessary. The parts list included:

1. Meter with 100A shunt
2. Off-On switch
3. Case for meter and switch (Case dimensions: 5-1/2" x 3-1/8" x 1-1/2")
4. 25 ft. 4-conductor cable
5. Automotive fuse holder (I used a fuse from my kit)
6. Miscellaneous connectors.
7. Note: for details, see the parts list at end of this post. 

The most difficult part for me was determining where to mount the meter. I had decided that I wanted a surface mount case, so I could remove the meter in the future and leave no trace. Determining how to run the 4/C cable was also a bit of a challenge. I decided to route it behind the fiberglass side panel, into the coach along side the door, then behind the side panel and exiting just below the 120VAC/12VDC power distribution center. This required the temporary removal of the rear passenger seat. Lots of screws.

Passenger seat removed, propane furnace exposed

With the passenger seat removed, it was possible to remove the side panel, and pull the cable behind the panel. I pulled the cable from the battery compartment to the passenger seat area, and re-assembled the interior panel. I left a foot lomg "pigtail" for connecting the meter.

Cable at Passenger Seat

I then mounted the rear of the meter case to the wall. I used 3M Dual Lock™ General Purpose Reclosable Fasteners. Note the female electrical connectors on the cable from the battery compartment:

Base of Meter Case

I assembled the meter in the case. Marked the case and cut the opening with a Dremel tool and cutting wheel. I used connectors so I can remove this if necessary. The "female" end goes on the cable from the battery compartment. The "male" end is in the meter case. This is so there should not be any exposed live parts if I pull the meter, even if the fuse at the shunt is intact.

Meter and Off-On switch in case

This is the front of the meter and switch, assembled in the case:

Front of meter case with Off-On switch

I mounted the meter to the case mounted on the wall:

Meter case mounted to the wall

This is the shunt, which was supplied with the meter. For the meter I purchased the shunt is connected between the negative battery post and the negative conductor. The shunt is rated 100A/75mV. The shunt is actually a precision resistor and the higher the current flowing through it, the higher the voltage drop across it. The voltage drop is 75 millivolts at 100 amperes.

Shunt

The shunt was installed in accordance with the manufacturer's instructions. A right angle screwdriver is helpful for installing the wiring to the shunt (I used a phillips).

CAUTION - Installing the shunt requires removing the negative battery lead. Exercise great care not to short a tool from negative to the nearby positive terminal. DEATH OR INJURY CAN RESULT. Be sure there is no battery load when doing this procedure.

The shunt is connected directly to the negative battery post. The black (Negative) cable is connected to the other side of the shunt; the yellow arrow points to that connection. Three of the leads of the 4-conductor cable is connected to the shunt. The fourth conductor goes to the red (Positive) battery terminal.  I installed an automotive fuse between the positive battery terminal and the lead going to the meter. That is to protect the wire in the event of a short circuit

CAUTION - A properly sized fuse is necessary to protect the wire in the event of equipment failure or short circuit. Fire, damage,  injury or death can result from an unprotected circuit.

Shunt installation and automotive fuse on positive battery terminal

With the installation complete I threw the "Off-On" switch to the "On" position.

I checked the display using a precision digital VOM. I measured the mV at the shunt and calculated the meter reading. The meter agreed.

Meter Setup
The meter has alarm points and some options:

1. Set backlight off or on. The default is "on".
2. Set voltage alarm threshold. The meter includes both "high" and "low" voltage alarms. These are set independently. The presence of an alarm flashes the backlight alternating "off" and "on". I set the low voltage alarm at the 50% DoD level for my coach batteries.
3. Set the measuring range. This meter will work with a 50A/75mV shunt or a 100A/75mV shunt. I set this to match the installed shunt, which is 100A/75mV.
4. Energy reset. The meter will accumulate and store kilo-watt hours (kWh). This value can be reset to zero.  

Meter Limitations
The meter is a DC meter. This means that the ammeter measurement is polarity sensitive. The meter as connected can only measure discharge current from the battery across the shunt. When charging the meter displays 0.00 amperes. However, by reversing the connections it is possible to measure charging current. I tried this and it works.

It was interesting to watch the Tripplite inverter/charger step through the charging levels. I may add a DPDT switch for this purpose, but it is completely optional. I've monitored the Tripplite by watching the AC current; as the Tripplite throttles back the AC current decreases. However, other 120VAC loads will mask that.  It is also possible to pull the compartment cover over the Tripplite and observe the charge state LEDs:

Green = Full Charge

Detailed Parts list, my cost $36.45 plus tax and any shipping:

1. MICTUNING DC 6.5-100V 0-100A LCD Digital Display Ammeter Voltmeter Multimeter Volt Watt Power Energy Meter Blue with 100A/75mV Shunt, Part No. MIC-DVG-015.
2. Serpac black plastic case, model 151i, BK.
3. Rocker switch, Philmore No. 30-882.
4. 4-conductor shielded cable, 24 AWG. (Use #22-24 AWG; smaller AWG is easier to pull).
5. Insulated terminal disconnects, male and female (from toolbox, not included in price total).
6. Fuse and fuseholder to protect the wire from the meter to the (+) positive battery terminal. Size of the fuse is determined by the size of the wire. 

New Voltmeter-Ammeter-Wattmeter for AGM batteries - Part 1

Earlier this year I replaced the AGM batteries in the Roadtrek with new AGMs. I decided against lithium (LiFePO4) batteries for the time being. For one thing, I hadn't decided which real estate I would give up. I wasn't sure I'd put them in the battery compartment as it is outside the rig and uninsulated.

I've posted on social media (G+ and FB) that I wasn't happy with the 4-point L-F-G-C "idiot light" arrangement in the Roadtrek, in particular because I discovered that the "G" or "Good" indicator was illuminated even when the batteries were below 50% depth of discharge (DoD).

What was my issue? It was about battery life and capacity. To get optimal life from AGM batteries most experts recommend not allowing the battery to regularly fall below 50% state of charge (SoC). The "G" or "Good" LED extinguishes below that level. The "F" or "Fair" light on the Roadtrek is below that. A simple plug-in digital meter was an option and one can be purchased for between $5 and $15. Here's one:

12V Plug-in digital Voltmeter

Our rental rig had such a simple meter, and I could plug one into the rear cabinet above the entertainment center in our 210P, which had a cigarette lighter for the 12V amplified antenna. I added a "Y" connector for this purpose. However, I also wanted an ammeter and a wattmeter, but I didn't want to spend the amount necessary for a Trimetric and I wanted something easy to install.

Here's the 12V connector I used to install a "Y" cable. That allowed me to connect a meter in addition to the 12V TV antenna amplifier. But viewing the meter in this location isn't very convenient.

Location of simple plug-in digital meter connector:

12V Connector in rear compartment

Installed and functional digital meter:

New Digital Meter

Battery Life Issues
All of this is really about getting full value and maximum capacity from the batteries. As AGM batteries age, they will lose capacity. Such batteries have specifications based on specific conditions, such as an ideal temperature of 77F. AGM batteries operate on chemical principles, and chemistry is influenced by temperature.

I had noticed that, after 4 years the batteries in the Roadtrek didn't seem to be able of providing the desired voltage for the time I wanted to use them "off the power grid". That indicated a loss of capacity.

The entire point of adding a digital voltmeter-ammeter is to get a better idea of the condition of the coach batteries. Even better than battery voltage is specific gravity, but that can't be readily determined. Below is a table for my current batteries which provides some idea of the life of the batteries when discharged repeatedly to certain levels of DoD (depth of discharge). As can be seen, the 50% DoD provides about 1200 charge-discharge cycles. Decreasing to 80% DoD provides a life of about 700 cycles. Avoiding DoD below 50% provides a good compromise between battery life (cycles) while providing adequate capacity.

The problem we face is that to extend battery life we either use them less (fewer cycles per year means more years of service before reaching end of life). Or, we can reduce the DoD. As noted in the table below, if the DoD is only 20% it is possible for a battery to provide 3600 charge-discharge cycles. Of course, to achieve only 20% DoD requires much less use of the available battery capacity.

Why Measure Battery Volts and Amperes?
How long can we run things in the coach on batteries and avoid discharging the batteries below 50% DoD? The ammeter and voltmeter with the tables for our batteries can be an aid to this.

For example, my batteries can provide 18.33AH for 12 hours. However, that is to 100% discharge, which is what I want to avoid. 50% DoD will allow a draw for only about half that time, or about 18.33AH for 6 hours.  Or, I could reduce the load and extend the time. If I really need to run solely on batteries for 12 hours, my batteries can provide about 9 amperes per hour:

                                           220AH/12H = 18.33A
                                           18.33A x 50% = 9.165A

The times are approximate. If we have an ammeter we can determine what the actual current draw on the batteries are. If we have a voltmeter. we can determine the state of charge of the batteries.

Battery Life and Charge-Discharge Cycles

Depth of Discharge - New AGMs

Using the Voltmeter
The digital voltmeter will provide an indicator of the state of charge (SoC) of the batteries. "OCV" is open circuit voltage, or the state when the batteries are not connected to a load:

Relative State of Charge @ 77F - New AGMs

Note that SoC tables may vary. Here is a "typical" AGM table, which differs from the chart above.

Typical AGM battery SoC table

Battery Life 
Taking care of batteries and extending their life will obviously reduce costs. They are expensive. 220AH of AGM batteries is about $450 to $600. However, the other desireable thing is capacity. I want to be assured that the battery is capable of providing the amperes I need for as long as I need them. A battery with reduced capacity may not be able to do that.

Capacity is the ability of a battery to deliver the amount of power it was designed to do. Over time, battery capacity will decrease. As the battery nears end of life, it's capacity will diminish significantly. The batteries I have are designed to provide 25A @ 460 minutes  (7.7 hours) when new. As the batteries lose capacity, they will provide 25A but for shorter periods of time. And as the battery discharges, the voltage will decrease. A battery with diminished capacity will experience more rapid voltage fall-off. DC power is volts x amperes. As the voltage diminishes, so does the power if the amperes are constant.

While extending battery life does reduce operating costs, I am more interested in having the desired capacity available to me.  My batteries are rated 220AH. That means that they can continuously provide about 18 amperes for 12 hours, if they can provide full capacity (see notes):

220AH/12H = 18.33A.

Real World Capacity
The capacity achieved is based on battery condition, ambient temperature and other factors.

As noted above, the 12 hour rating for my AGM batteries is 18.33A.

In the real worlds AGM battery capacity does gradually decline, and by 700 cycles capacity decrease to 50-60% is usual. That means that the above number will gradually decrease:

• New AGM battery (80-100% capacity) = 18.33A for 12 hours
• Battery after 400 cycles (80% capacity) =  14.7A for 12 hours.
• Battery after 700 cycles 50-60% capacity = 9.2A for 12 hours

Lithium batteries also have a gradual reduction in capacity, but generally a 220AH battery:

• Lithium battery after 400-500 cycles (80% capacity) = 14.7A for 12 hours. 

Note: The above numbers are based on battery manufacturer published data and this information does vary from manufacturer to manufacturer. It is important to realize that battery data is usually under ideal conditions such as 77F temperature. AGM battery capacity decreases as battery temperature decreases and can perform (charge and discharge) over temperature ranges of (-)4F to 104F. Lithium batteries generally can operate with charging temperature of 32F-113F and discharge temperatures of (-)4F to 140F. Electric vehicle and experimental data indicates that high environment temperature could accelerate the aging of LiFePO4 batteries, while low temperature could reduce output power capability. Data suggests normal life can be achieve if operated in the range 50F to 104F.
However, it is important to check with each manufacturer for their specifications.

Battery Life based on Depth of Discharge
A well maintained AGM (absorbent glass mat) battery has a life of 6-8 years. Average life has been stated to be 3-5 years. If not maintained, that will diminish to 2-4 years. Note that it really is charge-discharge cycles that are the limit. Battery manufacturers assume a certain number of such cycles in a year. That assumes optimal temperatures of 77F and that the batteries are immediately charged to 100% immediately upon the end of the discharge cycle.

For example, with 50% DoD my batteries are designed to provide 1200 charge-discharge cycles:

1. If used every day, a battery will experience 365 cycles per year.  Under such use, the batteries have a service life of 3.2 years. 
2. If a charge-discharge cycle occurs every other day, or about 180 times a year, the same batteries could provide a service life of 6.7 years. 
3. If a charge-discharge cycle occurs every three days, or about 120 times a year, the same batteries could provide a service life of 10.0 years. 

 For example, with 80% DoD my batteries are designed to provide 700 charge-discharge cycles:

1. If used every day, a battery will experience 365 cycles per year.   Under such use, the batteries have a service life of 1.9 years.  
2. If a charge-discharge cycle occurs every other day, or about 180 times a year, the same batteries could provide a service life of 3.9 years. 
3. If a charge-discharge cycle occurs every three days, or about 120 times a year, the same batteries could provide a service life of 5.8 years. 

How does one "maintain" a maintenance free battery?

1. Recharge as soon as possible after use - preferably within 24 hours.
2. Recharge the battery properly.
3. Use a "smart" charger.
4. Battery should not be charged if the core temperature reaches 120F (49°C).
5. Avoid discharging below 50% SoC (state of charge).
6. When recharging, recharge to at least 80% SoC before beginning another discharge cycle. 
7. Charge to 100% as often as possible. 
8. Avoid heat; heat shortens battery life. Each 15°F (8C) rise in temperature reduces the life of the battery in half.
9. Know the correct state of charge (SoC). Knowing this will help to extend overall cycle life. A battery monitor is worthwhile and use one that is accurate.  

Battery Cost 
There is a cost to overtaxing batteries, as noted above. Best case is a battery with 50% DoD, and that yields 1200 cycles under best conditions. As noted above:

1. If used every day, or 365 cycles per year or a service life of 3.2 years.  The cost is $140 per year ($450/3.2)
2. If a charge-discharge cycle occurs every other day, or about 180 times a year, the same batteries could provide a service life of 6.7 years. The cost is $67 per year ($450/6.7).
3. If a charge-discharge cycle occurs every three days, or about 120 times a year, the same batteries  could provide a service life of 10.0 years. The cost is $45 per year ($450/10).

 For example, with 80% DoD, which provided more AH, but sacrifices battery life:

1. If used every day, a battery will have 365 cycles per year.  At 80% DoD, my batteries are designed to provide 700 cycles.  Under such use, the batteries have a service life of 1.9 years.  (Cost is $236 per year)
2. If a charge-discharge cycle occurs every other day, or about 180 times a year, the same batteries with a life of 700 cycles could provide a service life of 3.9 years. (Cost is $115 per year).
3. If a charge-discharge cycle occurs every three days, or about 120 times a year, the same batteries with a life of 700 cycles could provide a service life of 5.8 years. (Cost is $78 per year).

Notes: 
Ampere-Hours. An amp hour (AH) rating is a rating usually used on deep cycle batteries. It is an ampere rating taken for 20 hours. For a 100 AH rated battery a load may draw 100AH from the battery for 20 hours.For such a battery, that's about 5 amperes an hour. 100AH/20H  = 5A).

1. The total time of discharge and load applied is not a linear relationship. As the battery load increases the actual capacity decreases. For example, a 100 AH battery with a 100 amp load should provide one hour of runtime. But it won't. The capacity of the battery will be severely reduced.
2. Each battery manufacturer provides AH data under various loads. For example, here is the table for my batteries, with a final voltage of 1.75V per cell (3 x 1.75 = 5.25V, or a dead battery):
1. 20 hours = 220 AH
2. 10 hours = 210 AH
3. 5 hours = 190 AH
4. 3 hours = 175AH
5. 2 hours = 155 AH
6. 1 hour = 130 AH

Using the AH from the battery table, a rough guide for capacity can be determined. For example, 10 hours = 210AH. To achieve a 50% DoD, 210 x 0.5 = 105AH realized capacity. To achieve a 80% DoD, 210 x 0.8 = 168 AH realized capacity.  However, these figures are approximate and are based upon a new battery and 77F. The approximate condition (state of charge, SoC) can be determined with a voltmeter.

Using the above, the 10 hour ability of the batteries is actually about:

10 hours, 50% DoD = 105AH/10H = 10.5A.
10 hours, 80% DoD = 168AH/10H = 16.8A.

Note that the above information is in accordance with the battery data provided by the manufacturer of my batteries. The actual data will vary by manufacturer.

August 10, 2017 added and expanded "real world" battery life data.

Current Project - Adding a DC Voltmeter-Wattmeter

Updated August 4
I completed the install yesterday. I did install a fuse at the coach batteries. I'll post a more complete blog in the future on the details of the install. The meter works well. I set the low voltage alarm at 12.1V (about 50% depth of discharge, or DoD). The meter is very accurate. I measured the voltage at the coach batteries and compared to the display. I also measured the mV at the shunt and compared to the ammeter display (has a 75mV shunt). After charging the coach batteries I killed the AC to the coach and with the meter powered, the fantastic fan at speed 1 and an overhead fluorescent on, this was the display. The battery voltage is high because it has some surface charge:

Voltmeter-ammeter-wattmeter with voltage alarm

Updated August 1

Meter in Case, with DC power "Off-On" switch

Making progress. The cabling is in, the shunt is mounted, and I've wired the meter case. I should complete in another hour or so. However, today (August 1) it was overcast and so I worked on the travel trailer; I'm using Meguiar's® Fiberglass Oxidation Remover on the cap. Got about 70% complete before the rain came in. I'll be working on that for another couple of days, weather permitting. Can't do this in the sunlight, or the rain. After completing with the Remover I'll be using No. 45 Polish followed by No. 56 Pure Wax.

Today I wired the meter case, and assembled jumper cabling to extend from the coach batteries to the cable run to the meter.



Original Post, July 28, 2017:
Current project is to put a decent DC electrical meter into the 210P, to monitor the coach batteries.

The 4-LEDS (L-F-G-C) or "Low-Fair-Good-Charging" indicate G "good" at 11.95V, which is not good IMHO. I really don't know the point at which the G indicator goes out, and the F "fair" indicator is illuminated. I don't think I want to find out.

Why my concern? The 11.95V which the LED "G" indicates "good" charge level, is actually a 40% charge level (60% DoD, or "Depth of Discharge") for the AGM coach batteries. Why do I consider that to be a problem? To get best life out of the AGMs it is my understanding that one should not repeatedly discharge below 50%, although these batteries can be discharged 80% (11.66V). The bad news? Doing so repeatedly will shorten the life. How much? As much as 50%, or a 5-8 year battery will make only 2.5-4 years.

So I'm interested in knowing the DoD and a good voltmeter will tell me that. My 210P has the AGM coach batteries, and I replaced the first set a few months ago; they were about 4-1/2 years old.

Is there an alternative approach? I considered just adding meter jacks, but G would have had some difficulty with that, so I'm putting in a digital ammeter-wattmeter. Probably the most difficult was determining how and where to mount it, because routing the cabling is a real pain. After figuring it out I purchased the parts. Should be up and running in a few day, assuming I find some time to complete.

Coach Battery Replacement

My Roadtrek which I could name "Tried and true" or "Rock steady" continues to perform. But there is maintenance to do. Some of this is preventative.

It became apparent that I needed to replace the coach batteries when one of them dropped to 0 volts. It had shorted, I guess, because the bank was at 6.5 volts, which was the voltage across one of the batteries and also the voltage across both. One battery seemed to be doing okay and the other was a tag-along. Just like America, 50% are doing the work and the other 50% is contributing nothing. beyond lip service.

I was aware that the batteries were not able to deliver the designed capacity. Capacity is the ability of a battery to provide the required power (watts) or ampere-hours for the required amount of time. My coach battery capacity prior to the 0 volt failure was below 50%, even though they measured suitable voltage on the indicator in the Roadtrek.

My batteries achieved a life of 4 years. Well maintained AGM batteries can go for 6 years, or more. I use a 50 watt solar panel with de-sulfating controller to maintain the batteries when off of the grid. My measurements indicate this is sufficient when storing the Roadtrek. On a sunny day the batteries will reach peak voltage. After a couple of cloudy days the voltage might decrease to about 80% as an indicator of "state of charge." I take my measurements early in the morning, prior to sunrise and after sufficient time to dissipate any "surface charge."

I'd done a lot of research including opening a discussion via the FMCA Roadtrek International "cyberrally" email.

I'd also designed a LiFePO4 system, should I want to upgrade to a lithium battery system. However, I decided at this time that going with AGM battery replacement was the prudent thing to do. More on that decision in a future post.

I was spending some time in the Tucson AZ area, so I found a distributor who carried the 220Ah 6-volt AGMs I was interested in and would install them for an additional $30. The total price was irresistible.

One thing we observed was the ends of the crimp connectors showed some oxidation. Is that a problem? The oxidation is higher resistance than bright copper, and over time that oxidation will creep up the wire. Resistance is a voltage loss and a source of heat. After cleaning, the ends were again shiny copper.

The installer then applied liquid plastic via a glue gun to seal the end of the connector. This should prevent further oxidation.

The new batteries included lifting means. One of the reasons I didn't do this was the fact that the old batteries didn't have such a means. I was faced with either purchasing a strap, or wrestling with 63 pound batteries. I've stored the lifting means in the compartment with the batteries.

Here's the completed installation:

After several weeks of monitoring the battery voltage, and with the solar panel connected, it seems the new batteries are doing well, achieving maximum terminal voltage and sustaining it into darkness.

My Roadtrek which I could name "Tried and true" or "Rock steady" continues to perform.

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."

AGM Battery Alternatives

It's again that time of year when attention goes toward the coach batteries in the RV. When the RV is in frequent use, this is never an issue. Running the engine will charge those batteries, as will plugging into shore power.

However, in winter, some of us put our RV into storage. Those AGM coach batteries then self-discharge. Sulfation may occur and if the batteries are sufficiently discharged they may freeze and undergo permanent damage. In winter, our attention turns to the coach batteries. When spring arrives some of us may be unhappy to find that our batteries have only 75-85% of rated capacity, or less.

Is There a Better Way?
In my case, I installed a 50 watt solar panel and charging system to help those AGM batteries. I also installed a smaller solar panel to offset parasitic drain for the engine battery. Both of these have seemed to help. I went to the storage facility for my RT and the coach battery monitor indicated my coach batteries were in "fair" condition. That has been typical; I suspect my RV which was purchased one year after manufacture had damaged AGM batteries. My current interest is in getting the maximum benefit from whatever coach battery system I have.

On my most recent RV inspection the engine started fine and I charged the coach batteries for a half-hour. Not a lot, but intended to augment the solar charging system.

But is there really a better way? I think lithium batteries are the way to go. I've begun exploring this.

1. Smaller lithium battery systems have been proven in sailboats.
2. Faster recharge times. 
3. Lithium batteries have half the weight of the AGM batteries on a weight versus output basis; that's another 70 lbs. of gear, or improved fuel economy, in my case. Or more battery capacity at the same weight!
4. Lithium batteries, while more costly initially do have a higher number of charge-discharge cycles and can tolerate deeper discharges. In simple terms, they will last far longer than the AGM batteries. 
5. There is some evidence that lithium batteries cost less over the life of the battery than do AGM batteries. For anyone who intends to use a RV for 10 years or so, this is significant. 
6. Lithium batteries don't freeze at low temperatures and have the winter problems of AGM lead-acid/water batteries. In other words, fewer winter maintenance issues. Roadtrek states in their 2014 210P manual "AGM Battery Warranty....... is voided if AGM batteries are tampered with, topped off with distilled water or allowed to sulfate or freeze due to lack of charge."
7. Lithium batteries have lower self-discharge rates. In other words, they can be stored for extended periods at full charge and don't self deplete. 
8. Lithium batteries can tolerate deeper discharge than can AGM batteries.
9. AGM batteries have high ambient temperature restrictions.  AGM batteries are designed for an average annual temperature of 77F (25C). If the average annual temperature is 95F (35C) then the battery life will be reduced by about 50 percent. 

Improving Solar Response
I've also been researching improved solar panels and I've decided it would be pointless to put them on an AGM battery system.  Improved solar panels would benefit with an improved electrical storage system. In other words, the system is limited by the weakest link in the chain.

I'll continue my research and will post the upgrades as I make them.

Why Do Manufacturers Use AGM Coach Batteries?
That's a question you might ask. The reasons are straightforward.

1. AGM technology is well established and existing system designs are in place.
2. Alternative battery technologies, such as lithium, are at a higher initial cost. This increases the purchase price of the RV.
3. New designs will require engineering manhours which is an additional cost to the RV manufacturer.
4. Other technologies are new and are not well understood. In other words, while technically superior, some technologies have not yet been widely offered because the sales, marketing, management and engineering departments at RV manufacturers have not yet come to grips with the benefits.
5. It's a competitive world. Most users (RV buyers) compare total cost to overall performance. It's only after purchase that the limitations become apparent.
6. Leadership entails risks. However, most western companies are risk-averse. My company recognized this. We were leaders in our field and as president I would remind our employees that "There is the leading edge, and then there is the bleeding edge." I can say that we did find ourselves from time to time on the "bleeding edge." Good engineering, attention to detail and serious prototyping kept us and our clients from going over the edge. I would say that lithium batteries, which are well proven in smaller systems such as sail boats are not at all like what I was facing with hardware and software which didn't perform as expected. This isn't 2008, nor was the microprocessor invented only four years ago. This is 2015 and there are a lot of Tesla motor vehicle on the road, and lithium batteries are not uncommon on sailing vessels. Lithium batteries are entering the mainstream.  

AGM Batteries Sulfation, RV AGM Battery Care and Charging - Part 2

This is part 2 about care of AGM batteries in a "motor home." The previous post is part 1.

After a significant amount of research into the chemistry,  technology and charging of AGM batteries I became concerned about battery damage including sulfation and freezing the battery electrolyte. I want to achieve longer battery life and have 100% rated battery power available when I am off the grid and am not running the generator. I decided I needed to make an improvement and installed a solar panel and solar controller-battery charger for my coach batteries. This post looks more closely at the research that led to my decision. I'll provide in brief the why's, as well as some of the "do's and don'ts." I am not promoting any product here. This describes the issues and the solution I chose, and provides background information about that decision. This may be helpful to others.

I chose a 50 watt solar panel and a "Solar Charger/Maintainer/Desulfator" rated for use with solar systems up to 180 Watts. The solar panel is not used when the vehicle is in motion. I decided on this approach because:

1. The replacement price of the coach batteries would be about $250.00-$400.00
2. The Camper Van may be stored for weeks and sometimes for months
3. It's desired to achieve the maximum life from the coach batteries
4. It's desired to have the batteries provide the maximum rated power throughout their life
5. When stored,  120V shore power is not available. Solar power is the only available power option unless the generator or vehicle motor is running.

The following post provides, in brief, what I have learned on this subject and how what I learned has influenced my decision  Why would I want to do this? I'd like to spare the reader the time to replicate what I have researched.

How to Achieve Full Life and Power from AGM Batteries
That is the goal. Get maximum power and longest life from the AGM coach batteries. Doing so should provide a more pleasurable trekking experience and reduce the annual cost of operating the camper van.

Deep Cycle AGM Batteries require complete charging, but not overcharging to achieve full lifespan, avoid freezing damage and provide the amount of power expected from them.

Roadtrek states in their 2014 210P manual "AGM Battery Warranty....... is voided if AGM batteries are tampered with, topped off with distilled water or allowed to sulfate or freeze due to lack of charge."

Here are the most important things that dictate battery life:

• Preventive maintenance
• Depth-of-Discharge (avoid discharge below 75% charged)
• Charging to a full charge
• Temperature conditions of the batteries (cooler is better). Batteries are designed for an average annual temperature of 77F (25C). If the average annual temperature is 95F (35C) then the battery life will be reduced by about 50 percent. 

What is full life? It varies. 3-5 years is fairly typical according to published information. However, AGM batteries are reputed to achieve up to 10 years if properly maintained, kept cool and if used in such a manner to maximize battery life. I decided I would prefer to replace these batteries every 6-8 years instead of every three years. I also decided I do want the maximum battery power to be available when needed.

Avoiding Sulfation and Extending Battery Life
Sulfation if left unchecked will kill the coach batteries. Sulfation begins when the batteries are not fully charged, and storing them unless "float charged" continues the sulfation process. The RT and most RVs include charging systems for the coach batteries. However, there are periods in which these 120V or engine and generator powered charging systems are not available. That is a problem. So how can I achieve my stated goal of long life at maximum power from these batteries under my actual storage and charging conditions?

Frequent charging while avoiding overcharging of AGM batteries will reduce, but not eliminate sulfation. Sulfation occurs each time a battery is discharged. Storing a battery is reputed to cause self-discharge and sulfation, and this is more serious at higher temperatures, above 75F.  Batteries which are not used weekly may experience sulfation.

Sulfation is the gradual coating of the positive lead plate of the battery with lead sulfate (PbSO4). Simultaneously the battery electrolyte, which is sulfuric acid (H2SO4) on losing SO4 molecules becomes diluted by water. This occurs during battery discharge. The chemistry is oxygen molecules (O2) from the positive lead plate combine with hydrogen molecules (H2) from the battery acid and the result is water (H2O).

Because AGM batteries are chemical devices, cold weather will slow the sulfation process while hot weather speeds it up. In other words, full charging may be more important at higher temperatures. On the other hand, as sulfation occurs battery electrolyte (acid) is diluted by water molecules and will freeze at lower temperatures than the normal electrolyte of a fully charged battery. Such freezing can damage the battery.

Normal charging does not remove all sulfate molecules from the plates. Over time they build up on the plate and ultimately contribute to the demise of the battery. Sulfation, or the formation of lead sulfate can permanently reduce battery capacity. If unchecked it can kill the battery.

Keeping batteries fully charged and reducing sulfation will extend the life of the batteries and provide optimum capacity. Battery life expectancy is directly the result of how well these batteries are maintained and how they are used (or abused). Key points are:

• Don't overcharge.
• Don't undercharge
• Keep fully charged and don't store undercharged.
• Use and keep the batteries at their average design temperature.  
• Apply a periodic full-saturation charge to de-sulfate the batteries.
• Don't over-deplete; reduce the average "depth of discharge." and avoid "deep discharge".
• Reduce the number of "discharge-charge" cycles. 
• Don't charge if over 120F and don't charge if the battery is frozen. 

Some of the above might not be possible. That is why many batteries don't survive for more than 3 years according to some published sources. However, I'm convinced that good care and attention to these details will extend battery life for most users. One manufacturer of battery chargers/maintainers/desulphators claims that certain models of their product "can more than double the useful life of new batteries." I can't verify that. However, it's prudent to ask why some batteries fail within 3 years while others go on for 6 or more years.

It is my understanding there are two types of sulfation: 1) reversible (soft sulfation), and 2) permanent (hard sulfation). Reversible sulfation is normal and can be corrected by a specific charging regimen. When charging, the PbSO4 is converted to lead and the SO4 combines with hydrogen to form electrolyte. Non-reversible sulfation occurs when a battery has been in a discharged condition, or "low state-of-charge" for a longer period, be it weeks or months. In such a state the sulfate crystals become permanent, cannot be reversed by charging methods and the capacity of the battery is permanently reduced and impaired.

Charging and Reducing or Reversing Sulfation
Special charging techniques are reputed to reverse sulfation.  Battery charging states include:

• Bulk (high, constant current)
• Absorption (constant voltage)
• Float (hold at 100% charge)
• Equalization.(controlled absorption overcharge)
• De-sulfation

A microprocessor "smart" charger will include three or four of these states. Special chargers provide a fifth state called "de-sulfation." One charger manufacturer declares "Patented high-frequency pulse desulfation is designed to reverse and eliminate battery sulfation."

There is some controversy about the claims of "reversing sulfation." One critic states "simple, electronic de-sulfation is a one size fits all approach." On the other hand, I've seen no comments or evidence that such pulse desulfation techniques can harm the batteries.

How to Apply a "Full Saturation" Charge
Such a charge is a general recommendation for lead acid batteries. However, some AGM battery manufacturers have specific requirements of this type of charge and if not followed it is possible to damage the batteries. This type of charge is also called an "Equalizing" charge. This is done by a deliberate overcharge of the batteries. The problem with sealed AGM batteries is there is no way to measure the electrolyte condition and so the equalizing charge is guesswork and may be based on terminal voltage. My guess is it's better to use a good 4-stage charger and avoid deep discharges.

Choosing a Battery Charger
The charger included in your RV or camper van is probably a three-stage "smart" charger which includes bulk, absorption and float stages.  "Float" charging is not "trickle" charging; a trickle charger can overcharge batteries!

I decided to add a "Charger/Maintainer/Desulfator" which was designed for use with solar panels. I also selected a solar panel which is overcapacity. This approach compensates for the lowered solar power that is available when daylight is minimized, such as during winter hours or when overcast. It also provides for a higher charging rate when there is optimal sunlight available.

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.

Overcharging is to be avoided. I decided to use a solar charger that includes temperature compensation with float charging. The temperature sensor is attached to one of the battery terminals. This permits charging in cold and hot weather. The manufacturer states compensation works over the range 0F to 130F.

The solar charging system is only used when the batteries are not being charged via 120V shore power, generator power or via a running vehicle engine. It is intended to be used at any time the vehicle is stationary. The solar charger is connected directly to the batteries and operates independent of the position of the battery disconnect switch.

How Long Does it Take to Charge the Batteries?
The answer to that question is determined by the amount of sunlight available and the condition of the batteries. The purpose of the solar charger is to take the batteries from a condition of 85% to 90% charged to full charge, or apply a "topping" charge. Once at full charge, the goal is to "float" and desulfate the batteries while avoiding overcharge. Temperature compensation reduces the float charge as the battery temperature increases.

To bring a discharged battery to full charge can take 7 to 10 hours or longer. That is not the purpose of the solar system, but if there is sufficient daylight hours such charging is a possibility.

How Does "Depth of Discharge" Influence Battery Life?
Any AGM battery has a service life which is measured in number of discharges and the "depth of discharge." As a rule of thumb, the less the "depth of discharge" the longer the life of the battery, but it should be discharged to 90% peak when used. In other words, if used the battery should be discharged 10% and  a battery which is repeatedly used and discharged to 50% of its peak capacity and then completely recharged may be usable for 1000 cycles. If one cycle occurs each day, then the battery may have a life of 3 years.

That same battery, if discharged to 75% of its peak capacity each day and then fully recharged may be usable for 2000 cycles. Under such conditions the battery may have a life of 6 years.

Furthermore, that same battery if discharged to 25% of its peak capacity each day and then fully recharged may be usable for 500 cycles. Under such conditions the battery may have a life of only 16 months. Discharging a battery to less than 25% capacity is to be avoided.

What are Battery Storage Choices?
Batteries can be disconnected and then charged if they are not going to be used for long periods of time. It's best to store the battery in a cool or cold place (sulfation is slowed when it is below 75F). Here's a few methods:

1. Turn the battery switch "off" and then connect a 3- or 4- stage microprocessor controlled battery charger and fully charge the battery. If the charger includes an automatic "float" mode it can be left connected to the battery for long periods of time. Check your manufacturer. 
2. If the battery is fully charged connect a "float" charger, again check your manufacturer.
3. Alternately, the battery can be removed in the vehicle and kept above freezing while a float charge is applied. 

Avoiding the Freezing of Batteries
If the electrolyte in a lead acid battery freezes, the battery will probably be damaged. The capacity of such a damaged battery will be reduced. What are the freezing temperatures of a depleted battery? A battery in good condition that is 100% charged has the maximum concentration of sulfuric acid as electrolyte. As the battery discharges, the concentration of the acid is reduced as water molecules replace acid molecules in the electrolyte. Here are typical freezing temperatures for lead acid batteries at different charge states:

100% Charged = (-) 77F, or (-) 67C.
75% Charged = (-) 35F or (-) 37C
50% Charged = (-) 10F or (-) 23C

Other Sources
There are a lot of web based sources on AGM battery maintenance and charging. Enter  "AGM battery maintenance", "AGM battery charging" or "AGM Battery desulfation" in your favorite search engine and you'll get a list.

AGM Coach Battery Issues - Do It Yourself Solar Charging

This post looks at achieving the maximum life and performance from AGM batteries and also the steps an owner who doesn't have access to 24/7 120V charging power can take to keep the batteries in his/her "motor home" at full charge. It includes some of the background information I used to decide on solar power for charging batteries, and it includes a short video.

The Problem
Many motor homes and camper vans include coach batteries. Depending upon how many batteries are included and their capacity, they can be used for powering many things. Typical uses include the water pump, interior and exterior lighting, the refrigerator and small appliances via an inverter. Some motor homes include solar panels for recharging of these batteries. Some do not.

Absorbent Glass Matt batteries, or AGM batteries are very different from the old lead-acid and gelled electrolyte batteries. AGM batteries have a thin fiberglass mat or screen between the lead plates. The fiberglass mat is saturated with acid and is compressed and sandwiched between the plates. This tight packing makes the interior components tolerant of vibration. They are ideal for use in moving vehicles.  Many AGM batteries include bolt-on terminals which are reputed to give a more reliable connection.

AGM batteries are not cheap, but the best ones can last longer than other, less costly batteries. Perhaps 5 to 8 years if given proper attention.

As with all things, there are pros and cons. This post will look into some of these. Part 2 will delve more deeply into batteries. This post addresses the need to keep AGM batteries fully charged.

AGM - Are all Deep Cycle?
Not all AGM batteries are alike. Some are designed to be what is called a "deep cycle" battery and others are not.  So what is a "deep cycle" battery? Such a battery is designed to be discharged and recharged many times. "Deep Cycle" means the battery can be discharged to a lower level of peak capacity and recover. Some manufacturer's state that a deep cycle battery will last three to four times longer than a starting battery under the same conditions.

The batteries I am concerned about are deep cycle batteries.

Advantages of AGM Deep Cycle Batteries
If properly maintained, these are some of the advantages of these batteries:

• Improved resistance to shock and vibration
• Totally sealed
• Reliable
• No acid fumes
• No spilled acid
• No need to add water
• If fully charged can tolerate freezing temperatures (temperatures as low as -40F, but check with your battery manufacturer)
• Longer life as compared to a starting battery

How Do I Maintain a Deep Cycle AGM Battery?
That's a good question and as these are expensive batteries they do need to be properly maintained to achieve their full design life. These are sealed batteries so there is no water to add. Does that mean that the battery is "maintenance free?" No, it does not.

So what do I have to do? Most important is to keep these batteries properly charged! For motor homes or campers which are plugged in each day, this should be rather easy because these vehicles include chargers powered by the 120V shore power. Some vehicles charge the coach batteries when the vehicle engine is running. Others include solar charging systems. Some vehicles include all of the above and a gasoline or propane generator which can also recharge the batteries! However, sulfation remains a problem in lead-acid batteries. More on that later.

The two things to do to achieve long life from AGM deep cycle batteries are:

1. Recharge daily to a full charge.
2. Don't discharge too low. Don't fully discharge.

Is AGM Battery Maintenance Important?
Yes it is. Roadtrek has this statement in the current 210P manual:

AGM Battery Warranty Batteries are warranted by the battery manufacturer for one year from the "In Service Date" of the Roadtrek. 

1. Warranty is voided if AGM batteries are tampered with, topped off with distilled water or allowed to sulfate or freeze due to lack of charge. 

So there you have it. Owners must keep their coach batteries charged. Roadtrek has specific instructions about this for dealers, too. Here's two photos showing the stickers on a 2013 210P. The notice about the "Deep Cycle Gel Battery" is specific (this Roadtrek did have AGM batteries):

Charging AGM Batteries When Storing the Motor Home
For anyone who stores their motor home for long periods of time, there are only three ways to get the power necessary to charge the batteries:

1. Shore Power - 120V plug-in connection.
2. Solar Power.
3. Frequent vehicle or generator use. 

However, not all storage facilities include the necessary 120V power for charging, and not all motor homes include a solar power charging system. If you are like many who store their motor homes, you may not start and use the vehicle for two, four or more weeks. Is this a problem? Yes it is. So what to do? One possibility is to remove the batteries and charge them in your garage. However, that might not be easy as these weigh about 70 lbs. each. I decided the most effective method to allow storing the vehicle outdoors with the batteries inside was to install a solar panel and a solar battery charger. That's what I did, and I place the solar panel inside the vehicle when in use for charging. No rooftop installation required! A video is included in this post.

Solar Power Charger and Sulfation
When the batteries are not being drained by daily use, it's possible to keep them charged if there is sufficient solar energy (daylight) available. For anyone who only has access to solar energy during vehicle storage, this might be the only way for daily recharging.

Will using solar energy and a charger avoid sulfation and are there other issues? In a later post I'll give a more thorough description of what sulfation is. For now, suffice it to say that during battery discharge sulfate molecules (SO4) move from the battery acid (electrolyte) to a lead plate to form crystals of lead sulfate (PbSO4). This is called "sulfation." This interferes with the ability of the battery to perform. It reduces battery capacity, which is simply stated the amount of power a battery can provide. Less power means you run out of power for your camper van electrical devices sooner than expected.

A second problem is as the battery discharges the acid concentration decreases and the electrolyte changes slowly to water. This makes the battery electrolyte more susceptible to freezing. Freezing can damage the battery. Uh, Oh!

What Type of Solar Controller-Charger?
I decided to purchase a controller which the manufacturer states has the following features:

• Full-time automatic battery desulphation
• Uses US Patented pulse battery desulfation technology
• One year unconditional money back warranty and five year "no hassle" warranty on parts & labor
• Plug and run operation - fully automatic easy efficient operation
• Never over-charges - you can keep it plugged in for weeks, months, even a year 
• Temperature compensation - prevents over and under charging from freezing to 130 degrees
• Solar battery charger maximizes battery life and capacity and reconditions weak batteries. Maintains up to 2 batteries at a time. Short circuit, spark and polarity protection. 
• When used as a maintainer....is guaranteed to maximize your battery's life and storage capacity. 

Installation Issues
Finding a convenient place to install the controller and near the batteries can be challenging. The charger manufacturer states "....it is important the controller be in the same general temperature environment as the battery(s)." The temperature sensor lead length is not to be altered and that placed a further restriction. I decided I didn't want  a rooftop mounting of the solar panels at this time. I concluded that a larger wattage solar panel could be put on the dash to charge the batteries via a solar controller-charger. I decided on a 50 watt panel because this would provide sufficient power under lower light and reduced daylight hours, such as in winter or with the windshield not clean. It would allow the controller to charge the batteries even on overcast days. I also wanted simplified controller mounting and wiring.

The manufacturer of the charger-controller says this about mounting the solar controller-charger:

IMPORTANT INFORMATION ON USING PRODUCT OUTDOORS: Weather-tight enclosure. Always mount units in vertical position with cord sets exiting downward to ensure weather tight integrity. Unit must be mounted this way to ensure long term trouble-free life including weatherproof integrity. Mounting in any other manner or using unmounted (parallel to ground) except indoors may cause unit to fail due to water intrusion that is unable to drain correctly to avoid damage. 

Installing a Solar Charging System
So how to go about this? Three things are necesary:

1. Solar Panel
2. Solar Controller - Charger
3. Interconnecting cables

Here is a photo of the battery compartment of a Roadtrek 210P, model year 2013. It shows two AGM batteries. As you can see the battery compartment is very tight:

Here's a brief video of the installation of a Solar Battery Condition Charger and Controller with a 50-Watt solar panel: