Battery Size

[Mark_Harrington]

Hello all,
I'm new to all this RV stuff but jumping in and learning a lot from this forum. I have a 2016 Freelander and it only came with one 24DC battery. I have just purchased roof solar panels awaiting installation and a suitcase style portable solar system. To compliment this setup I need to add a second battery. I put a GC2 battery into the battery compartment and it fit, with the exception that the screw post terminals and fill vent pressed lightly against the foam insulation of the battery box lid/step top. I assume its a no go with such a tight clearance., If I raise the step top, how much venting room is needed?

[Blackhat6mike]

If U R going to use solar,u will need a lot more battery than a single group24. Two group 31s would be more like it. What good is it to have solar if you have no place to store your elec? I have 600 watts of panels and a MPPT controller with 5 grp31 bats. We boondocks a lot and rely on solar.


Sent from my iPhone using Forest River Forums Retired Army Pathfinder Vietnam vet.

[Mark_Harrington]

I would have a huge battery bank if there were room, but the battery box can only support 2, and not sure if they can even be 27's. It's just a bit larger than two 24 batteries

[Rbertalotto]

Can you fit two 6v golf cart batteries? You need as much storage as you can get.

[wanderer69]

Originally Posted by Mark_Harrington

Hello all,
I'm new to all this RV stuff but jumping in and learning a lot from this forum. I have a 2016 Freelander and it only came with one 24DC battery. I have just purchased roof solar panels awaiting installation and a suitcase style portable solar system. To compliment this setup I need to add a second battery. I put a GC2 battery into the battery compartment and it fit, with the exception that the screw post terminals and fill vent pressed lightly against the foam insulation of the battery box lid/step top. I assume its a no go with such a tight clearance., If I raise the step top, how much venting room is needed?

A GC2 is a 6 volt golf cart battery. you can't mix that with a 12 volt, You will need either 2 12v or 2 6 v. If you have the room or can make room get 2 6v golf cart batteries they will produce more amps.

[Blackhat6mike]

One more time. If you combine two 6 vdc batteries of 125 amp hr each in series, you have 12vdc @ 125 amp hrs, NOT 250. The 125 amp hrs is at 6vdc, not 12vdc.
If you combine two 12vdc batteries of 125 amp hrs each in parallel, you will have a total of 250 amp hrs @12vdc.
You will find this on several threads here on the forum. It's a common miscalculation.

[boondocking]

I think what wanderer69 is saying is you will have more amp hour capacity with two 6v batterys compared to two 12v of the equivalent physical size and weight.

[Blackhat6mike]

My sailboat has 8 x 6vdc batteries for the house and 2 x 12vdc batts for cranking [diesel] so this isn't my first rodeo. If I could trade out all the 6vdc units for 12vdc batteries, I would do it in a heart beat, but the battery compartment was designed for the 6vdc setup.
A 12vdc battery of the approximate size same size as a standard 6vdc, will not have very many amp hrs to play with and the 6vdc will out weigh it by far.
I have 5 x 12vdc batteries in my bank in the TT and can't imagine what the weight would be if I used 6vdc units. It's just what fits your personal needs and weight/size parameters. Just remember there is a core charge for each unit and if you lose a 6vdc battery in the system, you are shut down. Lose one 12vdc and you just lose amp hrs, but you are still online.
Different strokes for different folks. My golf cart has 12vdc bats.

[boondocking]

"I have 5 x 12vdc batteries in my bank in the TT and can't imagine what the weight would be if I used 6vdc units."

In discussing weight and amp hours. Your 12v Group31 weighs 69 lbs and is rated at 100 AH and a 6v that weighs 68 lbs is rated at 245 AH.

So if we do the math.

Your TT battery bank weighs 345 lbs with a capacity of 500 AH and a total of 5 batterys. The equivalent with 6v batterys would be 4 batterys weighing 272 lbs with a capacity of 490 AH.
That is 73 lbs more with a 12vdc bank and almost the same capacity (10 AH less).

[Blackhat6mike]

All of my 12vdc batteries are rated 125 amp hrs or above. The way I figure it, that's 625+ amp hrs.
The 6vdc batteries in my boat are 180 amp hrs weigh 71 lbs each. Where can you get a 6vdc battery that stores 245 amp hrs?? I've bought a lot of 6vdc batteries in my time but never seen one that big. Even then, connected two each in series then paralleled, that would total 490 amp hrs @ 12vdc.
That is 135 amp hrs difference or the equivalent of one large deep cycle 12vdc battery.
Sorry, just not a fan of all those 6vdc batteries taking up so much space and all the core charges when they need replacing. My boat cost me a fortune every time I have to replace batteries and they are charged by a wind gen.

[dcheatwood]

Rule of thumb learned in electronics 101. "Current is constant in a series circuit." "Voltage us constant in a parallel circuit."

[boondocking]

Actually there is a lead acid battery made by Trojan that is even better than the 245 AH I mentioned. It is a GC2H, is 10.3 inches x 7.2 inches X 11.9 inches high, weighs 72 lbs and has a 20 hr rating of 260 AH. That has got to be an awesome battery.

[pgandw]

We just installed 2 Costco golf cart batteries - 6V at 232AH each. Cost $150 for the pair. Fit perfectly in a box where 2 size 24 80AH 12V batteries had been jammed - a little taller, but I had the height clearance. Now have 116AH available (50% of 232) instead of 80 (50% of 160).

My previous size 24 12V batteries got mismatched for charge, and caused a fire in my battery box from the venting gases and the melting connecting wires (#6 wire). Had to cut the wires to put out the flames (small).

If parallel batteries get even slightly out of synch charge-wise, the curents can easily get to the wire melting stage. I much prefer the dual 6 volt series setup in a towed, land-based camper where a failure ends the camping trip (absolute worst case). I have 50% more capacity than I had, and the cost was quite reasonable.

Fred W
2014 Rockwood A122 A-frame
2008 Hyundai Entourage (minivan)

[Rbertalotto]

When I added solar to my 19RR I wanted to up the battery capacity. I agonized over it for weeks (I tend to do that....)...Anyways, I decided I wanted no maintenance so I wanted AMG. I used two 110AH group 31 AMG batteries for a total of 220AH and 110 usable AH.

My rational was price ($179 each at Sam's Club) and if one battery failed while on a trip I'd still have 12V available.

[ScottBrownstein]

The 12 vs 6 argument has been going on in solar and RV forums for years. The best argument that I have ever heard, besides all of the math examples, is actually quite simple. A 6V battery has 3 cells and a 12 V has six. When you look at a constant volume to put battery capacity in, 2 12 volt units means you have 12 cells, and all of the plastic separators required to support them. 2 6 volt units have only 6 cells and leaves more volume for plates and electrolyte. In fact, equivalent volume 6V units generally weigh more than 12, which is certainly due to lead! In lead acid batteries, weigh is good! In addition, series charging is more controllable since if batteries have different internal resistances they will still charge in a series configuration while the parallel setup that is required for 12v can be problematic. My 335DS has 6-12 volt house batteries since it has a residential frig, I would have preferred 6 volt units but will have to wait a few years to replace them.

Finally, if one battery in a 12V parallel circuit fails you will have significant trouble maintaining anything on the others without disconnecting the failed unit.

[Rbertalotto]

Where were you Scott when I was agonizing!!!! That just makes perfect sense!

"For Sale...Two, like new AGM 12V batteries"