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Old 04-07-2022, 01:04 PM   #1
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Adding additional battery

We camp a lot without hookups. We have 2 100a/h size 27 lead acid batteries in the entry steps of our small Class C. I would like to add more battery capacity but there is no place near the original bank of 2. In addition, we also have 100w solar "suitcase" and solar controller in a storage area toward the back of the rig. As a short term solution I once used a sealed AGM battery to power a CPAP machine next to the bed. I connected it to the solar controller using an A/B switch. I was wondering if this could be a more permanent solution. My concerns have to do with safety, both ventilation and battery types.
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Old 04-07-2022, 07:14 PM   #2
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That should be safe. You probably loose a lot in the length of cable from panels through the switch. You would probably be better off having a jack near the AGM battery and plug portable panel directly to AGM battery or battery bank under steps. What you are doing is safe with an AGM battery.
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Old 04-09-2022, 10:18 AM   #3
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Thanks... My solar panels go to a PWM controller and then to the A/B/Both switch (which is 6 inches away). Then the "B" side of the switch would go to the AGM battery inside the rig (only 24" away). You said it would be better to have a jack from the panels directly to the AGM battery. Do you mean AFTER the controller? The A/B switch is very substantial (used in marine applications)
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Old 04-09-2022, 10:23 AM   #4
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Unless severely overcharged (voltage way too high) there is no out-gassing from AGM batteries. You are fine without ventilation.


What is what we use in the sailboat main saloon-- in a locker with no ventilation.
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Old 04-09-2022, 11:03 AM   #5
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Get rid of the lead acid batteries. They are 200 a/h, but in reality you cannot use all the battery capacity because once they get part way discharged the voltage is too low, and going down to near zero will both harm the battery (shorten its life) and only provide useless low low voltage.
So, a 200a/h batter of lead acid is really only 100a/h or less of useable power.

Instead, use lithium. You can get a 200a/h lithium 12v battery for under $700.
You will need to spend $ on a proper lithium charger, and/or a lithium solar controller, and maybe a dc to dc controller between batt and your vehicle alternator.
The result will be nearly 200 useable a/h of power, quadruple what you have now!
The lithium batteries will last 4x longer than lead acid too, or better, so after ten years you look back and realize big savings over FLA.
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Old 04-09-2022, 11:21 AM   #6
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Originally Posted by JDKouwe View Post
We camp a lot without hookups. We have 2 100a/h size 27 lead acid batteries in the entry steps of our small Class C. I would like to add more battery capacity but there is no place near the original bank of 2. In addition, we also have 100w solar "suitcase" and solar controller in a storage area toward the back of the rig. As a short term solution I once used a sealed AGM battery to power a CPAP machine next to the bed. I connected it to the solar controller using an A/B switch. I was wondering if this could be a more permanent solution. My concerns have to do with safety, both ventilation and battery types.

On our Class C , we replaced the 12v house batteries with 2 - 6v GC2 batteries wired in series . These batteries are designed to provide full power over an extended period of time .

We replace the batteries after 5 years for $250 . I usually sell the old batteries that are still in great shape for $50 ea. to boaters . So in ten years we've spent $300 on house batteries .

This requires nothing more than hooking them up to the MH .

We researched the Li-ion before going with the 6v GC2's and determined that our style of camping wouldn't justify the additional cost .

Li-ion requires a significant amount of additional cost due to charging profile , controllers , initial cost of batteries , maintaining storage environment such as when cold weather camping . The Li-ion do not handle cold well .

Just my 2 cents FWIW.
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Old 04-09-2022, 11:42 AM   #7
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Of course there are multiple solutions and some are more or less costly and more or less efficient.

Group 27 batteries may be 70 or 80 amp hours each. When they need replacing, see if you can't install larger higher capacity AGM's or lithium. Possibly group 31 AGM that would be 100 to 110 amp hours each. Check available space. Mixing lithium and lead acid is not a good solution, so do all or none.

The AGM you have can be permanently installed in the space under the bed. Protect the terminals from mechanical damage and possible electrical short. The battery can be put inside a typical cheap plastic battery box. The box must not be sealed. I built a wood box in mine to take up less space.

Technically you can connect the under bed AGM to the built in RV charger/12 volt system. There will be some inefficiencies, but no catastrophic failures. All three batteries will provide power to the CPAP or other RV appliances.

You can also connect the solar controller to the built in 12 volt system. Solar will charge all three more efficiently.

Heavy gauge wire will be required to bridge the long distance. A fuse or circuit breaker in the heavy gauge wire is required.

The differences between AGM and flooded cell batteries are small. They both can work on the same charging profile and discharge using the same or similar voltage profile.

AGM batteries are usually sensitive to high charging voltages. Some battery charges produce more than 14.4 volts for some or all of their charging profiles. These high voltage chargers are not suitable for AGM.

Deeply discharged AGM batteries can be charged at 14.4 volts for a few hours. After that voltage needs to drop to 13.6 or so. AGM store better a 13.2 volts. Many modern RV smart chargers follow this charging profile. My WFCO charger does.

AGM batteries are better able to resist damage when drawn down flat. Flooded cells are less resistant.

If you were designing a replacement system, it would be more efficient to make all the batteries identical and provide a charger that is most efficient for that system.

Since you already have equipment, combining them may be a little less efficient. However you will get good service from a combined system. Just check your RV battery charger manual to make sure it does not charge above 14.4 - 14.6 volts. 15 volts or so would be too much.

I wish you good luck and happy trails ahead!
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Old 04-09-2022, 12:24 PM   #8
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Originally Posted by JDKouwe View Post
Thanks... My solar panels go to a PWM controller and then to the A/B/Both switch (which is 6 inches away). Then the "B" side of the switch would go to the AGM battery inside the rig (only 24" away). You said it would be better to have a jack from the panels directly to the AGM battery. Do you mean AFTER the controller? The A/B switch is very substantial (used in marine applications)
With the distances involved, your setup is fine.
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Old 04-09-2022, 05:54 PM   #9
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Thank you guys so much!
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Old 04-11-2022, 09:02 PM   #10
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Quote:
Originally Posted by Bill Gail View Post
On our Class C , we replaced the 12v house batteries with 2 - 6v GC2 batteries wired in series . These batteries are designed to provide full power over an extended period of time .

We replace the batteries after 5 years for $250 . I usually sell the old batteries that are still in great shape for $50 ea. to boaters . So in ten years we've spent $300 on house batteries .

This requires nothing more than hooking them up to the MH .

We researched the Li-ion before going with the 6v GC2's and determined that our style of camping wouldn't justify the additional cost .

Li-ion requires a significant amount of additional cost due to charging profile , controllers , initial cost of batteries , maintaining storage environment such as when cold weather camping . The Li-ion do not handle cold well .

Just my 2 cents FWIW.
The issues with Lithium and cold are only for charging, not use/ discharging. The discharge cut-off is well well below freezing, and very very few will be camping in such cold weather. To charge you typically need the batteries above freezing, so put them inside your RV (no off-gassing or anything so is safe) or use or get a battery(s) with built-in heaters that heat themselves before allowing themselves to be charged. Mainly, keep them inside the camper and they will always be warm enough, and they are big enough investment you will want to take care of them.

The cost per use (amp hour, watt hour) is way better with Lithium than AGM or Lead Acid, but it is not for the lightweight people who camp a few days per year at a campground with full hookups, a marine battery is sufficient for this level of camping. If you are wanting to do serious off-grid and extended camping consider nothing else except lithium and enough solar (300-400watts +) to power your trip.
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Old 04-22-2022, 04:19 AM   #11
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Hey, @JDKouwe, you can use this solution permanently. Compared to other cells, this is cheaper, and its lifespan is impressive. Once, I also tied this AGM battery to my CPAP accessories. It worked well, not to mention it was easy to change and manage.
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Old 04-22-2022, 04:42 AM   #12
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Your best to go with Lithium. Yes, they are expensive, but for dry camping, they are the best way to go. They also will outlast many lead or AGM battery changes.
This one is advertised to be of the same dimensions as the stock under the step batteries you have now. YOu can give them a call.They will let you know exactly what you will need to convert it over.
https://battlebornbatteries.com/prod...cycle-battery/
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Old 04-22-2022, 06:05 AM   #13
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If you are considering LiFePO4 read through this well written link and visit the video reviews of the guy mention.
https://marinehowto.com/drop-in-life...ated-consumer/
Both are pro LFP but have some very valid points IMO
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Old 05-07-2022, 07:44 PM   #14
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Lots of goo info and choices..
If you Boondock mostly then Lithium is a great choice..

If you have an idea of how many days a year you dry camp, and your use, you can estimate your charge cycles.. This will help decide your fate,,,

I use FLA, 2 29/31 under steps and I have one more in a compartment that I vented almost directly across the RV.. 7 foot of 2/0 postive cable to the other batteris and 4 foot neg to the frame point of the other negative..
BUT I do run them down to 30$ or so getting me 170-210 AHR in use before charging..
My use is less than 90 cycles per year,, .. I am on year 4 and they hold well..

I rarely have site power when camping but use a genny of sorts when I have too, 600 watts of solar helps.. also I updated the RV charger and that has improved battery life.

For my needs this works awesome..

If I was in need of more power storage then I would have 400 Ahr of Lithium. and another 200 solar.. for 800 that would in good sun replenish them after a 60-80% over nite heavy discharge rate. or at a lower full use,, blah blah. solar can get addicting too..
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