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Old 10-12-2021, 10:03 PM   #1
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Winter Camping, how to maintain batteries

Hey everyone!

I am a fairly new motorhome owner, my wife and I have been living full time in our Citation Supreme for the past 3 months and have been loving every minute.

Going into the colder temperatures, we have been experiencing some issues with our batteries (currently 2x 27RVS 12v deep cycle from Napa). After colder nights we are waking up to a barely working furnace fan, and completely dead batteries.

I want to make sure that we have this figured out properly before the actual cold weather hits!

I have installed a Renogy 2000watt inverter/charger and periodically run our 3000 watt generator to charge the batteries whenever they are running low, but we are now not able to make it through the night without issues.

I have always been told to remove batteries prior to winter seasons, but now that we are relying on them for our home, I am wondering how people make it work?

I've looked at silicone heating mats to keep the bay warm, rated at 350watts, but this alone would kill my batteries over a brief period. My battery bay is located under my unit, so it isn't heated very well by our furnace.

I do have plans to skirt the unit, but I don't believe this will be enough to solve our issue.

I now am looking to purchase a set of 2 6v golf cart batteries, and have the option of going with flooded lead acid, or AGM. Ranging between 220-260 aH per battery.

Does anyone have any insight into whether flooded lead acid or AGM perform better in cold temperatures? Or if either is even a feasible option?

Will new 6v batteries be enough to make it through the night for us, or is there other solutions that I am overlooking?

With the new 6v batteries, I am considering adding a 100w bulb or some other type of heating device to keep the bay warmer. It simply seems like a lose-lose situation, spending battery power to keep the batteries warm, in order to not lose battery power

Thanks in advance everyone and happy camping
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Old 10-13-2021, 06:14 AM   #2
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IMO you are on the right track, at least partially.
A pair of GCs are a good choice for deep cycle use.
I prefer AGM but there is a premium $ for the convenience of maint free.
Where I disagree is if you are using the battys dont worry about keeping them warm and expending AHs to do it.
I would use / get a digital meter and check your A draw with typical o'nite loads and figure what size batty bank you need. I am guessing the GP 27s aren't enough for your needs and will need more. The measurements above an an estimate of % time running furnace will give you an idea how many AH you will need overnight.
Just remember with two 6V battys in series the V adds but AH remains the same (approx 200 AH +/-)

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Old 10-13-2021, 08:38 AM   #3
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Part of the problem you'll run into is that lead acid batteries "slow down" when they get cold. A rough rule of thumb is at freezing the batteries "lose" about 25% of their capacity vs 75F. They're not damaged, warm them up and they're fine but just expect the the colder they are, the less you get.

Also important is adjusting the charge parameters for cold batteries. They need a higher voltage to get a complete charge and if the charger isn't automatically compensating for that, you'll end up with undercharged batteries. So between that and reduced capacity you have a double whammy of reduced output. On top of that, if left this way too long they'll be damaged by this chronic undercharging.

Warming the batteries solves a lot of this but as observed, this energy comes from somewhere. One option would be to insulate the enclosure they're in, and use a heat source that's powered by generator. Since you need to run a generator anyway to charge them this is when they'll be heated, and between thermal mass and the insulated enclosure they should stay plenty warm enough between charge cycles.

Doing a capacity test will tell you if you have a battery problem or charge/load problem. All the remedies in the world won't help if these batteries are shot. This isn't your basic clamp on 2 minute test at the car parts place, do a timed discharge into a known load and come up with a real Ah value. From there you can better judge your capacity vs usage and can decide what the best solution will be going forward.

Mark B.
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Old 10-13-2021, 09:03 AM   #4
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Ok thank you Winemaker2! I will need to do some testing and see what we are expecting for output over the night, I expect this to increase as the weather continues to cool off and the furnace runs more to keep up.

You mentioned when wired in series the v adds to 12, but not the case with aH? This is some unfortunate news to me. If I choose 2x6v golf cart batteries, both rated at 220 aH (https://www.cdnrg.com/products/G2300), my total aH would be 220 and not 440?

To confirm, my current 2xRVS are rated at 100 aH each, so I would really only gain 20 aH over my current setup?

From what I understand, the golf cart batteries can be discharged to 80% without damage which is another added benefit. I've heard so many people raving about the increased capacity of moving to golf cart batteries but the numbers don't seem as impressive without adding up the aH, am I overlooking something here?
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Old 10-13-2021, 09:24 AM   #5
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Part of the problem you'll run into is that lead acid batteries "slow down" when they get cold. A rough rule of thumb is at freezing the batteries "lose" about 25% of their capacity vs 75F. They're not damaged, warm them up and they're fine but just expect the the colder they are, the less you get.

Also important is adjusting the charge parameters for cold batteries. They need a higher voltage to get a complete charge and if the charger isn't automatically compensating for that, you'll end up with undercharged batteries. So between that and reduced capacity you have a double whammy of reduced output. On top of that, if left this way too long they'll be damaged by this chronic undercharging.

Warming the batteries solves a lot of this but as observed, this energy comes from somewhere. One option would be to insulate the enclosure they're in, and use a heat source that's powered by generator. Since you need to run a generator anyway to charge them this is when they'll be heated, and between thermal mass and the insulated enclosure they should stay plenty warm enough between charge cycles.

Doing a capacity test will tell you if you have a battery problem or charge/load problem. All the remedies in the world won't help if these batteries are shot. This isn't your basic clamp on 2 minute test at the car parts place, do a timed discharge into a known load and come up with a real Ah value. From there you can better judge your capacity vs usage and can decide what the best solution will be going forward.

Mark B.
Albuquerque, NM
Thanks Mark, that makes a lot of sense.

My inverter/charger has a temperature probe that sits between my batteries to adjust charging based on temp, so I'm happy that is covered.

I spent about 2 months at a serviced location plugged in, prior to installing the inverter/charger. Meaning my old stock converter was doing the job of charging, which from what I understand could have damaged my batteries by improper charging.

I have also just learned that I have been discharging these past 50% which could have also caused damage.

I now wonder if a big part of my problem is that my current batteries may very well be damaged. I will be following your instructions to test the current aH of my batteries and report back!

Really appreciate you guys taking the time to help, thanks again!!
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Old 10-13-2021, 10:01 AM   #6
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Quote:
Originally Posted by Logik View Post
My inverter/charger has a temperature probe
"Check"

Quote:
my old stock converter was doing the job of charging, which from what I understand could have damaged my batteries by improper charging.
It would have to be pretty old to be the kind that tended to cook batteries.

Quote:
I have been discharging these past 50% which could have also caused damage.
The "50%" point does not damage batteries. Going below 80%DOD (100% of Ah) can. Improper charging, storage and maintenance of batteries are the top three killers of batteries. It is very difficult to wear a battery out by cycling provided you care for it otherwise. If these are "RV/Marine" batteries they don't enjoy quite the durability of a true deep cycle and would be less tolerant of "less than optimum" usage (i.e undercharging and being run dead).

Quote:
my current batteries may very well be damaged. I will be following your instructions to test the current aH of my batteries and report back!
It comes down to charging them 100%, putting a C/20 load on them and seeing how long they run until they reach 10.5V. I use an inexpensive inverter and a couple of 120V light bulbs selected to draw the proper current.

Not sure if your inverter/charger can serve as a battery monitor (something besides volts). If not, an inexpensive battery monitor will go a long way towards managing power. I think you'll discover that no matter what batteries you have you're not running your genset enough. If you anticipate that you'll be running at a perpetual partial state of charge, you might look at batteries designed for solar energy storage. Or just get used to the idea that your batteries may not get "optimum" service life compared to ones that are consistently recharged 100%. Lithium is an option too, they tolerate long term states of discharge pretty well but have acquisition and integration costs to consider.

Mark B.
Albuquerque, NM
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Old 10-13-2021, 10:54 AM   #7
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my old stock converter was doing the job of charging, which from what I understand could have damaged my batteries by improper charging.

It is unlikely your old converter was damaging your batteries. Almost all RV converters are high quality chargers.

However, many high end chargers let you change charging parameters. If that was done poorly, then no telling what happened.

More often than not, not storing fully charged causes battery damage. Fully charge lead acid batteries 14 to 18 hours before storage. Fully recharge again before terminal voltage drops below 12.4 volts.

I have also just learned that I have been discharging these past 50% which could have also caused damage.

Deep draw batteries are designed for repeated discharge down to 10%. Most lead acid deep draw batteries can be drawn down to 10% and recharged between 200 and 400 times. That is how they are tested.

Drawing down to 50% counts as 1/2 discharge cycle so you may get between 400 and 800 cycles.

I now wonder if a big part of my problem is that my current batteries may very well be damaged. I will be following your instructions to test the current aH of my batteries and report back!

This is an excellent first step. Knowing where you are starting is important.
Battery capacity and energy conservation are likely solutions to your problem.

I get 3 days of winter dry camping when using my pair of 100 amp hour 12 volt AGM batteries (200 amp hours total). You probably need more to heat your larger RV.

I have installed a Renogy 2000watt inverter/charger and periodically run our 3000 watt generator to charge the batteries whenever they are running low, but we are now not able to make it through the night without issues.

Charging lead acid batteries using a generator is always a challenge. Running the generator for a short time is always desirable, but lead acid batteries take a long time to charge.

How much current can your new 2000 watt inverter deliver for battery charging? A 200 amp hour AGM set can use 50 to 60 amps. A 400 amp hour set can use 100 or more amps for fast charging.

How long do you run the generator for when you charge? A full clean 100% charge takes 14 to 18 hours. A 90% charge may take 4 to 6 hours. An 80% charge may take 2 to 4 hours. For the 80% charge, this of course, depends on the current capacity of the charger.

AGM batteries tend to do the initial bulk charge faster. Flooded cell gulf cart batteries are cheaper to install, but usually take longer to do the initial bulk charge. Lifeline brand AGM's are among the best performers.

I've looked at silicone heating mats to keep the bay warm, rated at 350watts, but this alone would kill my batteries over a brief period. My battery bay is located under my unit, so it isn't heated very well by our furnace.

As posted above using the batteries to heat the batteries is self defeating. The mats and battery blankets are usually used for charging lithium batteries or for engine start batteries when shore power is available.

Flooded cell battery bays must be open to ambient air because they emit hydrogen gas while charging.

I now am looking to purchase a set of 2 6v golf cart batteries, and have the option of going with flooded lead acid, or AGM. Ranging between 220-260 aH per battery.

As posted above, a pair of 6 volt 260 amp hour batteries provides 260 amp hours at 12 volts. You would need 4 to significantly increase your capacity.

Does anyone have any insight into whether flooded lead acid or AGM perform better in cold temperatures? Or if either is even a feasible option?

AGM batteries tend to charge faster
AGM batteries can be installed inside the cabin since they do not normally emit hydrogen gas or spit acid. The battery bay can be enclosed (not sealed) for better temperature control.
AGM batteries tolerate deep discharge better than flooded cells. They can even be drawn down flat a few times without affecting their capacity significantly.

Lead acid batteries perform well at below freezing temperatures. They can be charged at higher voltage when cold, but discharge slower. A bigger battery bank will mitigate the cold effect. They don't loose amp hour capacity so much as they loose peak output capacity (cold cranking amps). This is less important for running an RV furnace.

Will new 6v batteries be enough to make it through the night for us, or is there other solutions that I am overlooking?

Doubling your amp hour capacity will double your furnace run time. Energy conservation is always helpful. Solar can help, but winter in Canada is not the best time for Solar performance.

With the new 6v batteries, I am considering adding a 100w bulb or some other type of heating device to keep the bay warmer. It simply seems like a lose-lose situation, spending battery power to keep the batteries warm, in order to not lose battery power

Most people agree. It is a lose-lose situation. Lithium battery banks are often heated while charging, but not while discharging. AGM batteries can be installed in an occupied heated space, but not flooded cell batteries.
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Old 10-13-2021, 07:02 PM   #8
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I dont know the specifics of your 12V GP 27 battys but doubt they are true deep cycle battys, comparable to GCs that are designed for deep cycling. You may not get a large increase in AHs making the switch but I would say the expected life of the GCs should be much better than the GP27s.
Hard to beat 4 6V GCs if you have the space.

I'm a fan of AGMs but I dont think they are inherently better than FLA in colder temps. You might check your batty temps under use as just using the battys wil, provide some internal heat. I doubt using batty power to heat them will even be neutral, more likely a net loss.
The only plus with AGMs is if you had an interior space to relocate them AGMs do not outgas H2 / acid like FLA and could be relocated to a warmer location... or just insulate the current space well (while still providing some ventilation)
In theory AGMs will accept a higher charge acceptance rate than FLAs but that would likely mean upgrading to a significantly larger charger to get any advantage and it only holds true during the initial bulk charge as during absorption the V is held constant and the A decreases as the batty charges. See link for the complete analysis and all the gory details...
https://marinehowto.com/how-fast-can...ry-be-charged/

Which brings up one last point I dont think has been mentioned. If you run battys down to 70% - 80% DOD you need to have a way to get them back to 0% DOD / 100% SOC in order to repeat it the next night. Many under estimate how long it takes to get a batty back to 100% SOC as the rate slows down significantly as you get above 80% and even more above 90%. Are you prepared to run genny 12- 14 hours/ day? Not getting battys back to 100% SOC is not good for battys and you will lose capacity permanently if left at reduced SOC for extended periods.

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Old 10-14-2021, 07:04 AM   #9
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As posted above using the batteries to heat the batteries is self defeating.
...
Flooded cell battery bays must be open to ambient air because they emit hydrogen gas while charging.
You can have your cake and eat it too. Insulating batteries amounts to using some closed cell sheet foam ('pink' or 'blue' from home improvement stores) underneath and around the sides. The top can remain open for venting, as there's an air gap underneath the top and heat will not conduct out readily. The foam is impervious to acid. I make a foam box by cutting the foam and butt gluing the joints with silicone. Or, just use enough sheets to fill in the gaps inside the enclosure - you can't have too much. Put the heating mat underneath or alongside the batteries inside the foam and whatever heat you add will stay in there pretty well. You'd only need to run the heat whenever there's generator or shore power, there'd be plenty of thermal mass and heat retention to maintain elevated temperatures between charge cycles. Flooded batteries will self heat to some extent but that requires some pretty hard cycling (extended high discharge currents) which isn't happening here, so I'd go with some form of external heat source. Moving the batteries to a controlled environment like under the bed or dinette would also check the box if extended cold weather operation is going to be the norm. AGM or lithium can both be safely operated in heated space.

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Old 10-14-2021, 07:30 AM   #10
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How ‘long are your nights’?
How many hours are drawing off the batteries each nite?
It’s very possible you are expecting too much of the battery set-up you currently have.
As others have mentioned, you may need to run your generator 10-12 hrs each day, if that’s the case, I would reverse it=run the generator all night when it’s the coldest, and use the solar, and batteries during the day when your usually out of the RV anyway’s. Just a thought.
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Old 10-14-2021, 07:55 AM   #11
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Winemaker2 said: "Hard to beat 4 6V. GC's if you have the space".
I agree and you certainly have the space. If you are going to skirt in the RV you could easily build an insulated battery box and place it under the RV and extend the cables etc. to add as many batteries as you see fit. I would add venting to the outdoors to anything you build. Especially with flooded batteries. While batteries are charging they give off gasses which are explosive and even a small ignition source can blow up a battery even for a while after they have been charged.
I would NOT recommend moving batteries inside an RV just for that reason. (Besides they stink)
Place batteries under a dinette and light your gas stove and you might level the entire RV.
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Old 10-16-2021, 01:28 PM   #12
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Quote:
Originally Posted by Logik
You mentioned when wired in series the v adds to 12, but not the case with aH? This is some unfortunate news to me. If I choose 2x6v golf cart batteries, both rated at 220 aH (https://www.cdnrg.com/products/G2300), my total aH would be 220 and not 440?

To confirm, my current 2xRVS are rated at 100 aH each, so I would really only gain 20 aH over my current setup?
Your two 12 volt'ers in parallel provide 100 AH each so at 50% depth of discharge on each one you only get half that to actually use, or 100 AH total.

Your two 220 AH in series would give you 110 AH at 50% depth of discharge so you really only gain 10 AH. But golf cart batteries typically hold the voltage higher for a longer period of time.

Quote:
From what I understand, the golf cart batteries can be discharged to 80% without damage which is another added benefit. I've heard so many people raving about the increased capacity of moving to golf cart batteries but the numbers don't seem as impressive without adding up the aH, am I overlooking something here?
Try comparing the Reserve Capacity numbers rather than Ampere Hours.

The Reserve Capacity test criteria is too deeply discharged for repeated usage because it drops the battery to 10.5 volts but if the battery manufacturers used the standard 25 amp constant discharge you can get an apples-to-apples comparison.

I just put in two "Dual Purpose" 12 volt AGM's rated at 200 reserve capacity minutes each. Here is the result of my testing, mostly with the inverter on and running one TV and the usual number of LED lights:

https://www.forestriverforums.com/fo...ml#post2638386

8 hours times 60 minutes at close to 1/2 of the 25 amp Reserve Capacity test current yielded 480 minutes of use, which is about on target.

"Dual Purpose", usually signified by "DP" somewhere in the part number, means they are a hybrid of deep cycle technology and starting technology. So they are equally poor at either usage.

We have a motorhome with an onboard generator so I need to assure my house batteries can start the generator reliably and in a pinch start the motorhome engine reliably. That's why I went with Dual Purpose batteries rather than straight Deep Cycle golf cart batteries. If I had the room for four golf cart batteries I would have gone that route but I do not have the space.

These are the golf cart batteries I was looking at but they are expensive: https://www.interstatebatteries.com/.../extreme-cycle

Hope this helps,

Ray
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Old 10-18-2021, 01:54 PM   #13
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Your two 12 volt'ers in parallel provide 100 AH each so at 50% depth of discharge on each one you only get half that to actually use, or 100 AH total.
What can't you actually use the other half?

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Old 10-18-2021, 11:55 PM   #14
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What can't you actually use the other half?
Each battery would be completely dead. When a six cell lead acid battery drops to roughly 10.5 volts the cells tend to reverse polarity and can become junk. That's why that Reserve Capacity test is done by the manufacturer down to 10.5 volts and why you should never go there.

12.0 volts is considered 50% discharged for a flooded lead acid battery and that's why you should not drop the battery lower. I have AGMs and have read that I can draw them lower but, as you know, electronics tend to get a bit wonky when they are designed for about 13 volts and you try to run them on low voltage. So there's no real point to do so.

This is why I have my generator auto start set to fire up the generator when the house batteries drop to 12.0 volts.

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