AGM Batteries for an RV - Which/Where/How/Why? (Discussion)

[dave_in_delaware]

... AGM's take some pretty serious over charging to make them vent. It would almost be impossible for the limited solar panel wattage you will be running to over charge them. There would have to be a catastrophic failure with the charge controller, and take a few days without using the batteries.

Alternator is another story and can over charge them if the voltage regulator fails

It's good to know that the AGMs can be kept inside an RV.

How frequent does a voltage regulator on an alternator fail? Is there a "backup" component or addition to the system that I could install to make sure the alternator doesn't overcharge?

For AGM batteries Concord makes the best and Trojan makes some pretty good ones. Stick with Concord, Deka, and Trojan for AGM.

Will do. Thanks for the advice!

1. Try to avoid parallel strings if possible. If you have to use parallel strings limit it to 2 strings or 2 12 volt batteries.

Just so I have these terms correct: Parallel strings is when you basically wire the + to another + and then that goes to a distribution panel? Compared to series where the first + goes to the next - and then that battery's + goes to the distribution? Is that what you're talking about? Like when you use two 6v batteries and wire them in series to get 12v?? I figured every 12v RV system wires in parallel?

Or are you talking about different wiring methods like here?

2. If you are going to use a generator or the vehicle alternator, you can go to a minimum of 2 day reserve capacity, but dot not go below that because that would require to discharge to 50%, and when you do that you are really cutting into the life cycle. At 50% you are looking at replacing the batteries every 2 years.

OK, understood. I'll limit my "max days boondocking" to 2 before I need to drive around to get the alternator charging the batteries again.

3. I noticed you are shooting for a huge amount of daily watt hour usage. You need to conserve more. Of course you can use the vehicle alternator to charge the batteries, but keep in mind it is inefficient. No problem if driving every day, but if camped out for long periods you might want to consider a small generator to conserve gasoline. Idling the engine just for electric power is a lot of over kill and uses a lot more gas then necessary. It is one thing to generate a couple hundred watt hours as that can be done in a few minutes on the alternator. But I heard you talking 2 or 3 thousand watt hours. That is 2 or 3 hours engine run time. A small generator requires the same time, but far less gas.

OK, point taken about the alternator and generator needs. Thanks!

I'm still working on reducing my power needs. I'm currently in contact with a company that has a water circ pump that can double for both the sink demand water and the hydronic heat. The trick with that is it only operates on 2-10v DC, so I'm not sure how that would work. I'm also still looking into a different heater or system for wintertime. I definitely want to use as little battery power as possible.

Also, when the info for an alternator says "155 amp" does that mean it'll generate 155 amps of recharge in one hour? And at what RPM would that be? I would assume normal driving RPMs (not idle, not revving).

[Sunking]

Yeah, I figured they were tied to each other and it was just the nature of the beast. I've read some posts on RV forums about lithium batteries, but they don't seem to be used all that much. My guess is the price might be a factor? I have no idea though. I haven't done any research on them.

You are correct it is the price, and to some degree a lack of equipment to support them

You say "under a coach" but you meant couch, right? So that's to say that the AGM's really don't vent any gasses and they're perfectly safe to have inside the van?

Yes I meant couch, my bad spell checker. AGM's take some pretty serious over charging to make them vent. It would almost be impossible for the limited solar panel wattage you will be running to over charge them. There would have to be a catastrophic failure with the charge controller, and take a few days without using the batteries.

Alternator is another story and can over charge them if the voltage regulator fails

The larger AGM batteries that I'm considering are not only heavy, but they're kind of tall. I'm debating in my mind which scenario would be better: put them inside under the couch/bed, or put them outside under the van. I suppose either location has its pro's and con's. But if they're under then I'd have to poke more holes into the van to get the wiring inside yet I'd save that much more space for storage. But if they're inside they'd have a little more capacity in the winter yet I'd lose that space to giant batteries. Hmmm.... Is it a 50/50 guess, toss a coin?


Are there any other brands of AGM that I should be looking at?

For AGM batteries Concord makes the best and Trojan makes some pretty good ones. Stick with Concord, Deka, and Trojan for AGM.

Some Advice:

1. Try to avoid parallel strings if possible. If you have to use parallel strings limit it to 2 strings or 2 12 volt batteries.

2. If you are going to use a generator or the vehicle alternator, you can go to a minimum of 2 day reserve capacity, but dot not go below that because that would require to discharge to 50%, and when you do that you are really cutting into the life cycle. At 50% you are looking at replacing the batteries every 2 years.

3. I noticed you are shooting for a huge amount of daily watt hour usage. You need to conserve more. Of course you can use the vehicle alternator to charge the batteries, but keep in mind it is inefficient. No problem if driving every day, but if camped out for long periods you might want to consider a small generator to conserve gasoline. Idling the engine just for electric power is a lot of over kill and uses a lot more gas then necessary. It is one thing to generate a couple hundred watt hours as that can be done in a few minutes on the alternator. But I heard you talking 2 or 3 thousand watt hours. That is 2 or 3 hours engine run time. A small generator requires the same time, but far less gas.

[dave_in_delaware]

Dave I can answer those questions. As for capacity it is pure physics you have to accept energy density of 40 wh/Kg or 18 wh/lb. This is why you hear so much about lithium batteries with densities up to 250 wh/Kg or 113 wh/lb. Weight and capacity are tied to each other.

Yeah, I figured they were tied to each other and it was just the nature of the beast. I've read some posts on RV forums about lithium batteries, but they don't seem to be used all that much. My guess is the price might be a factor? I have no idea though. I haven't done any research on them.

As for storage, under a coach is fine. If you ever smell anything like rotten eggs, ventilate the place. Heat destroys batteries, cold lowers capacity but preserves batteries.

You say "under a coach" but you meant couch, right? So that's to say that the AGM's really don't vent any gasses and they're perfectly safe to have inside the van?

The larger AGM batteries that I'm considering are not only heavy, but they're kind of tall. I'm debating in my mind which scenario would be better: put them inside under the couch/bed, or put them outside under the van. I suppose either location has its pro's and con's. But if they're under then I'd have to poke more holes into the van to get the wiring inside yet I'd save that much more space for storage. But if they're inside they'd have a little more capacity in the winter yet I'd lose that space to giant batteries. Hmmm.... Is it a 50/50 guess, toss a coin?


Are there any other brands of AGM that I should be looking at?

Thanks for your input, Sunking! I appreciate it.

[Sunking]

Dave I can answer those questions. As for capacity it is pure physics you have to accept energy density of 40 wh/Kg or 18 wh/lb. This is why you hear so much about lithium batteries with densities up to 250 wh/Kg or 113 wh/lb. Weight and capacity are tied to each other.

As for storage, under a coach is fine. If you ever smell anything like rotten eggs, ventilate the place. Heat destroys batteries, cold lowers capacity but preserves batteries.

[dave_in_delaware]

OK, I'd like to run a few ideas and questions past everyone here, to get opinions, tips, suggestions, do's, don'ts, etc.

So far in my Homebuilt RV Project, I'm figuring I'll need a few 12v AGM batteries for the "house" batteries, which will power all the lights, fridge, pumps, fans, etc. (and I'll be using solar panels and the engine's alternator for charging). I'm thinking I'll be purchasing something locally from a battery company just down the street (convenient), like:

Deka/"Astrolite" Group 31, 105 ah AGM (69 lb)
Deka/"Astrolite" Group 4D, 198 ah AGM (129 lb)
Deka/"Astrolite" Group 8D, 245 ah AGM (135 lb)

Obviously, the higher the ah the better, but with that also comes a lot more weight (and cost). Are there other brands or sizes I should be looking into? What is better - more smaller batteries or fewer larger batteries? Space becomes a key factor I suppose.

From what I've read on many RV sites and forums, the general concensus about AGM bateries is that they are maintenance-free, spill-proof, and do not vent any gasses (unless charged incorrectly). Assuming this is true, could they be placed under a couch or in a storage cabinet and not vented to the outside? Would this be safe if someone sleeps on the couch that the batteries are under? Or is what I read incorrect and they NEED to be vented because they do vent a little gas normally??

I've also read plenty about the temperature affecting the performance of batteries. I've been assuming that I'd have the batteries inside under the couch so they're warmer, but depending on the outcome of the above issues (venting), perhaps they'll need to be placed outside.

If they're outside the van (RV), I know many people who have mounted their batteries inside a battery box (usually behind the rear axle) or battery "hanger" frame made of steel angle. Since I live in Delaware (which gets all four seasons, including 105