Single 12v battery, or two 12v in parallel

[Tonybrown32]

Hi all,

New to owning an RV this spring, and have a 2015 Forest River Shamrock IKSS which we are enjoying...

We still have the original battery, and it needs to be replaced.. not sure how well maintained it was by the previous owner, but 3 years lifespan is about all we will get I expect anyway..

As I'm looking to replace the original group 24 deep cycle 12v battery, I'm contemplating just getting two group 27s, as I have room for both in the battery compartment on the tounge.

We only camp 3-4 times a summer... we like to have electric hookups, but many of the state parks here in WI have the electric sites all booked up well before we are ready to plan camping weekends so don't always have electric. We camp weekends, so maybe 2-3 nights max, and without hookups, the single group 24 doesn't last us the whole weekend, and generators aren't allowed in the state parks here...

I'm thinking it would be nice to have two 12v batteries, for 2 reasons... so that on short trips, we don't have to drain the battery as deeply.. and to make sure we have enough power to last us through 2-3 days.

I don't feel like we camp enough yet to justify the more expensive AGMs, and I doubt we will get that much more life out of them to justify the cost given the way we use them, so I've decided on average 27 size wet cells for my application.

My question is, should I just hook up one at a time, and then switch the terminals to my 2nd battery once the first is depleted to around 50%, or should I just hook them both up in parallel for simplicity?

I just plug the rig into the house power to keep the batteries charged up, and don't plan on updating or upgrading the converter, wiring, etc...

Pro's and cons? Any benefits to parallel vs. just switching to the "spare" battery?

Any comments or suggestion welcome.. appreciated!

[pgandw]

Two GC-2 (golf cart) batteries in series is a cheaper and better alternative to two 12V Group 24s. The GC-2s should also come out on top compared to Group 27s as well.

I ended up switching from a pair of Group 24s in parallel that destroyed themselves when one of them had an issue, compounded by my stupidity.

Both Costco and Walmart (or Sam's Club) sell Interstate GC-2 batteries for about $80 - $85 each. Probably want the one with the highest AH capacity. I've run mine (232AH from Costco) 3 years now, powering my A-frame while dry camping for up to 4 nights of moderate heater use without taking the batteries below 50%.

To answer your question directly, because lead-acid batteries are non-linear, you get more capacity for a given output when putting 12V batteries in parallel. However, you take the risk that an issue with one battery will take out the other before you even know what happened. You DO NOT want to parallel batteries that are significantly unequal in charge - the higher charge feeds into the lower charge at a cable-melting rate.

hope this helps
Fred W
2014 Rockwood A122 A-frame

[Tonybrown32]

Originally Posted by pgandw

Two GC-2 (golf cart) batteries in series is a cheaper and better alternative to two 12V Group 24s. The GC-2s should also come out on top compared to Group 27s as well.

I ended up switching from a pair of Group 24s in parallel that destroyed themselves when one of them had an issue, compounded by my stupidity.

Both Costco and Walmart (or Sam's Club) sell Interstate GC-2 batteries for about $80 - $85 each. Probably want the one with the highest AH capacity. I've run mine (232AH from Costco) 3 years now, powering my A-frame while dry camping for up to 4 nights of moderate heater use without taking the batteries below 50%.

To answer your question directly, because lead-acid batteries are non-linear, you get more capacity for a given output when putting 12V batteries in parallel. However, you take the risk that an issue with one battery will take out the other before you even know what happened. You DO NOT want to parallel batteries that are significantly unequal in charge - the higher charge feeds into the lower charge at a cable-melting rate.

hope this helps
Fred W
2014 Rockwood A122 A-frame

This is great information thank you... Interesting that two 6v batteries in a series would outperform the amp hours of two group 24 series 12v batteries...

After measuring more closely, I only have room for two group 24 batteries on my battery rack....

Another question then, if two 6v batteries in series is the better option than two 12v batteries, would I need to make any other modifications in my camper wiring other than the obvious differences in connecting in series? Would I be able to direct replace the 12v battery with the two 6v without any other wiring or converter/charger upgrades to my rig?

Thanks!

[boondocking]

No other modification would need to done if using two - GC-2 batteries.
The GC-2 is .5 inches wider and 2.4 inches taller than the Grp 24.

[Tonybrown32]

The more I read today, the more I find the redundancy of having two 12v batteries pretty appealing... knowing we only dry camp/boondock 2-3 nights max, and just a few times a year, I can fit one group 27 or 31 battery on my rack and keep the 2nd one in my truck bed... then swap out the depleted one for the fresh one once it drains to 50% or a bit more... or heck drain it to 80%, swap, and charge up after the weekend if generators aren't allowed.

It doesn't bother me if they only last 3-4 years... at $80-100 each its an acceptable consumable cost over that period of time.

If I have the generator along, the single battery will charge quicker when my camper is connected to the generator power, and I can also plug in my charger into one of the generator outlets to charge the depleted one at the same time if needed.

If one of the 12v batteries has a problem I still have the spare to get through a weekend conserving power or topping off with the generator if we have to.

Less tounge weight as well keeping only one battery connected on the rack rather than two 6v.

Seems like more benefits to having 2 larger 12v for our style of camping, vs two 6v. I don't have room for four 6v batteries, so not even an option.

[WolfWhistle]

Originally Posted by Tonybrown32

The more I read today, the more I find the redundancy of having two 12v batteries pretty appealing... knowing we only dry camp/boondock 2-3 nights max, and just a few times a year, I can fit one group 27 or 31 battery on my rack and keep the 2nd one in my truck bed... then swap out the depleted one for the fresh one once it drains to 50% or a bit more... or heck drain it to 80%, swap, and charge up after the weekend if generators aren't allowed.

Curious how you will know when you are at 50% or 20% (not 80%)? You can't go by instant voltage, because state of charge values are based on resting readings. I personally won't be without a good monitor. I can't imagine trying to keep up with battery voltages and swapping batteries around while camping. That makes me tired just thinking about it. You mentioned having 4 - 6 volt. Two (2) 6 volts are all that's needed and a strap to get them in series.
ww

[Tonybrown32]

I would keep it pretty simple and press the battery level button on my panel to see where I am at... it's next to the buttons that show me the levels in my tanks... full, 2/3, 1/3, or Empty.. it may not be that accurate, but I view the batteries as consumable anyway.. and likely needing replacement in 3-4 seasons...

I am not looking to spend much time meticulously maintaining them to get one extra season out of them or stressing too much about depleting to 80% instead of 50%.

At 1/3 left on my panel indicator I can spin 2 wing nuts off the depleted battery and plop in a new battery into the case on the tounge in about 5 min.

If I can use my generator, would just have the 2nd 12v along as a spare if I even want to bring it, and not bother swapping, just use the generator to charge up.

Doesn't sound too difficult to me... but I putz around a lot camping anyway...

Also, the old group 24 I am replacing lasted us almost our full 3 day camping trip last time out, so a 27 or 31 should get us through most trips without needing to swap, but nice to have the spare available so we don't have to conserve as much.

[camaraderie]

Ummm...a battery monitor and occasional watering can get 10 years out of deep cycles. But if you want to treat them like Energizers...that's your prerogative. AGMS will NOT last longer if treated i a similar manner so definitely don't waste your money on those down the road.

[Tonybrown32]

Originally Posted by camaraderie

Ummm...a battery monitor and occasional watering can get 10 years out of deep cycles. But if you want to treat them like Energizers...that's your prerogative. AGMS will NOT last longer if treated i a similar manner so definitely don't waste your money on those down the road.

Point well taken... I won't be totally ignoring the batteries... I just won't be worried to death if they go over half capacity... I do check the water levels regularly, keep them charged up when not in use, and at minimum check the battery level on the panel in my rig.

If I have two 12v batteries to work with, I'll be much more likely to only drain them to half way and switch, or at least not let them completely drain to zero like I do with my only single 12v I have now, so may get more life out of them than 3-4 I expect having just one to work with, and draining it to zero every time we use it.

[Jonol]

Use a $10. acid densety tester to check and your battery will last a long long time.
My 12v groupe 27 are 7 years old and still going good.

[johnbryanpeters]

Originally Posted by Tonybrown32

I would keep it pretty simple and press the battery level button on my panel to see where I am at... it's next to the buttons that show me the levels in my tanks... full, 2/3, 1/3, or Empty.. it may not be that accurate, but I view the batteries as consumable anyway.. and likely needing replacement in 3-4 seasons...

I am not looking to spend much time meticulously maintaining them to get one extra season out of them or stressing too much about depleting to 80% instead of 50%.

At 1/3 left on my panel indicator I can spin 2 wing nuts off the depleted battery and plop in a new battery into the case on the tounge in about 5 min.

If I can use my generator, would just have the 2nd 12v along as a spare if I even want to bring it, and not bother swapping, just use the generator to charge up.

Doesn't sound too difficult to me... but I putz around a lot camping anyway...

Also, the old group 24 I am replacing lasted us almost our full 3 day camping trip last time out, so a 27 or 31 should get us through most trips without needing to swap, but nice to have the spare available so we don't have to conserve as much.

The panel indicators are horrendously inaccurate.

To the original poster: For what you want to do and with your space limitations, two 12 V type 24s in parallel would make the most sense.

[WolfWhistle]

Not only horrendously inaccurate, E, 2/3, 1/3, Full - isn't what it means. It means Weak, Fair, Good, and Charge. A battery can be at 75% and these will show Good or even Charge. At least get one of these, or something like it.

https://powerwerx.com/panel-mount-di...CABEgJhH_D_BwE

If you have already made up your mind to do nothing and run a battery down to 20% why on earth are you asking for advice?
WW

[garbonz]

Peukarts law is relevant here. Short version, depletion of a battery is dependent on the ratio of the amps drawn to the size of the battery bank. SO, you will get better (slightly) performance out of a larger bank bank than 2 smaller ones.

Just saying.

In Order to know what is going on you need a Victron BVM 700 monitor or equivalent.

[WolfWhistle]

Originally Posted by garbonz

Peukarts law is relevant here. Short version, depletion of a battery is dependent on the ratio of the amps drawn to the size of the battery bank. SO, you will get better (slightly) performance out of a larger bank bank than 2 smaller ones.

Just saying.

In Order to know what is going on you need a Victron BVM 700 monitor or equivalent.

That is true, both points true. A single wet 12 volt 100Ah battery becomes less than 72Ah when discharged with a 15 amp load for less than 5 hours. Two together gives you about 14 hours with that same 15 amp load. Using one battery at a time could mean you need 3 batteries in rotation.

[Jonol]

Sorry but no Victor monitor will beet a $10. Acid densety tester!

[rk06382]

Originally Posted by Jonol

Sorry but no Victor monitor will beet a $10. Acid densety tester!

Battery hydrometer can only be used with a flooded wet cell battery.

Victron Energy BMV-700 series Battery Monitor can be used on any type of battery.

[Jonol]

I agree but I tought we are taking abought type 27 or 6 volts golf cart acid battery here.

[Radio]

I would do two things, whether you go with 2 6v or 2 12v.

Buy 2 identical batteries at the same place at the same time. Preferably from the same manufacturing batch. You want them as evenly matched as possible. (I'll spare you the sermon as to why)

Get a fairly heavy extension cord and keep the trailer plugged into power. Just enough to keep the batteries topped off. And check the fluid level on a schedule. My batteries are now 10 years old. No problem.

[rk06382]

Originally Posted by Jonol

I agree but I tought we are taking abought type 27 or 6 volts golf cart acid battery here.

A Coulomb Counter is the best way to gauge how many amps left in your battery system. Victron Energy Battery Monitor is one of the best but you can use a less expensive one.

Amazon: Coulomb Counter search

[Jonol]

You will never beet the presision of a acid densety tester for the price!