2 6v batters VS 2 12v

Mostly because 2 large six volt batteries in series gives you more amp-hours than the 12 V batteries do. For example Our 6V Interstates have a rating of 220 AH (amp/hour) each where a 12V might give 80-90 AH each for a total of only 160-180 AH (example). Plus the deep cycle battery handles deep discharge and recharge better.

Dave

It might also depend on your use case. I initially started with a bank of 6v Trojan T-125's, but wasn't satisfied with the voltage drop on heavy inverter draw. I switched to Rolls-Surrette high capacity 12v (210AH) to help mitigate that issue for me.

2oldman thanks for the links.

If a large inverter may be in use, 12 volt jars may have a slight advantage. Part of that may be due to the external series connection required for a 6 volt pair. Another part is 12 volt jars totaling up to the same amp-hour capacity have double the cell count, so each cell is working 1/2 as hard.

The downside is that as cell count rises the possibility of failure rises, too.

True deepcycle 12 volt may be more expensive per amp-hour.

Add some solar panels and your batteries may last even longer.

I'm a fan of AGM jars.

harley-dave wrote:
Mostly because 2 large six volt batteries in series gives you more amp-hours than the 12 V batteries do. For example Our 6V Interstates have a rating of 220 AH (amp/hour) each where a 12V might give 80-90 AH each for a total of only 160-180 AH (example). Plus the deep cycle battery handles deep discharge and recharge better.

Dave

Good answer, but keep in mind that pure deep cycle also comes in 12v sizes.

Cocky_Camper wrote:
I just replaced the house batteries in our Sea Breeze after getting 8 years out of them. It had to 6v in it. Just curious, why do some people run two 6 volts instead of parallel 12v?

Keep in mind that two 6's in series, is just one big 12 and granted, it's big, but then if you only have room for four batteries, you now have just two big 12's, rather than four smaller 12's.
Usually and unless you find some really large 12's that will fit, the four 6's will still have more capacity.
They they found this out, with putting four 12's in golf carts for awhile and have since went back to using six 8's, so again, pure deep cycle comes in multiple voltages.
Then we have the AGM's and my preference and even though expensive, they're maintenance free and don't expel gas. Also the ones that I have, came with a 60 month, replacement warranty, so we'll see how that goes, in a couple of more years.
Mine are four 12v AGM's, neatly connected in parallel obviously and the main reason for going this route, was for keeping it OEM, like the connection diagram on the compartment door and not like we boon dock for days on end, anyway. No matter what, you'll need to run your genset occasionally to keep them up, anyway.

harley-dave wrote:
Mostly because 2 large six volt batteries in series gives you more amp-hours than the 12 V batteries do. For example Our 6V Interstates have a rating of 220 AH (amp/hour) each where a 12V might give 80-90 AH each for a total of only 160-180 AH (example). Plus the deep cycle battery handles deep discharge and recharge better.

Despite what the distributors and retail establishments tell you, marine/dual purpose 12V batteries are NOT true deep cycle batteries. The only commonly available TRUE deep cycle batteries are 6V golf cart batteries.

(12V deep cycle batteries DO EXIST, but they are hard to locate (typically special order) and very expensive)

Trojan isn’t a distributor or retailer, wizard. The T1275 is a true deep cycle 12 volt battery.

http://www.trojanbattery.com/product/t-1275/

theoldwizard1 wrote:

harley-dave wrote:
Mostly because 2 large six volt batteries in series gives you more amp-hours than the 12 V batteries do. For example Our 6V Interstates have a rating of 220 AH (amp/hour) each where a 12V might give 80-90 AH each for a total of only 160-180 AH (example). Plus the deep cycle battery handles deep discharge and recharge better.

Despite what the distributors and retail establishments tell you, marine/dual purpose 12V batteries are NOT true deep cycle batteries. The only commonly available TRUE deep cycle batteries are 6V golf cart batteries.

(12V deep cycle batteries DO EXIST, but they are hard to locate (typically special order) and very expensive)

Where did you get this idea of 6v only, when you can go to Sam's or Cosco, and buy 8v golf cart batteries, all day long? Same for 12 golf cart batteries, but not so much now, since the industry quit using them for OEM. I'll take a look at Rural King, the next time I'm there for these, as well. As an added note, they haven't made 36v golf carts for years, but there's still many of them out there, including mine, for feeding the battery industry. With the four 12's golf carts, many have since installed the today's standard of six 8's.
Now, gels, are especially good and wouldn't mind having four 12's like these, installed in our coach.... 12v deep cycle gel
You're absolutely correct about marine batteries, not being true deep cycle, in any sense of the word.

Two part answer
Most 12 volt batteries are MARINE/Deep cycle. and should not be allowed to drop below around 75-80% state of charge

Groups sizes
24, about 75 amp hours total
27/29 Just under/over 100
30 120-130

That's total amp hours each. there are some differenced with is why the range and about.s

Now GOLF CAR (GC) batteries are TRUE deep cycle. you can talk them down to half full and a pair of GC-2 In series make one big 12 volt battery. about 220 amp hours give or take 10.

See the difference.. Way more usable power.

the DEEP CYCLE (GC) battery is more likely to survive and OH @!@@#! level discharge too (If promptly recharged).