12V vs 6V

SoundGuy wrote:

ktmrfs wrote:
If you dry camp a lot, then a pair of 6V has an advantage of more AH ...

Not necessarily ... a pair of G31 12 volt deep cycle batteries will offer similar AH capacity to a pair of GC-2 6 volt batteries. Apples to apples. ;)

ktmrfs wrote:
... and the ability to withstand hundreds of discharges to less than 50% of capacity. Something 12V aren't real good at.

Also, if you intend to run a very heavy load (>100A) like inverters etc. for > a few minutes at at time, and do it fairly often then 12V offer an advantage in that they have lower internal resistance and are much better at high current draw situations.

I would be interested in seeing supporting documentation to both these claims as my primary interest in upgrading to dual batteries from my current single G27, aside from the fact it's now 8 yrs old, is that I am now running a 1K inverter for those times we don't have on-site shore power available. My current single G27 has handled the task surprisingly well so far but a dual set of 12s or 6s would obviously make the most of what this inverter can do for us. As such I'd be interested in any further information regarding these two claims ... got any links? :@

looking at the Trojan website, cycle life if a pair of GC2's discharged to 30%SOC is around 500 cycles IIRC. So in terms of useable AH 6V has an advantage in cycle life and capacity over most 12V. Most 12V even the trojan's, cycle life degrades rapidly beyond 50%DOD. So a 250AH 12V has around 125 "useable AH" per cycle with reasonable life. While a 250AH 6V bank has 180-200 useable AH per cycle for the same or higher cycle life.

And how many of us will ever do enough camping to get to 500 cycles? Golf carts, yes, campers, not many of us.


Personally my last set of Trojan T125's were discharged to around 20%SOC (70%DOD) around 30 times per year for 8 years. 250ish cycles. Then I gave them to our daughters FIL. 4 years later, they are still doing fine and he has discharged them to around 40%SOC another 50 times.


As for high current discharge, myself and several others have gone through that with 6V. A pair of 6V will handle a 800- 1000W load down to about 80%SOC before dropping below the trip voltage on most inverters. Get's very frustrating when the bank needs to be almost fully charged to run the microwave for a few minutes. A single 12V will do better than that. for 1000W load, 4GC is a better choice. They will run 1000W inverter down to around 60%SOC. But a single or pair of 12V will do that as well will ease. and Four 12V will handle that with lots of margin.

I once did a load test on 4GC batteries, One of my 80AH 12V for my diesel truck will do 800CCA, 4 6V GC, over 500AH have a hard time doing that.

The tradeoff is cycle life. 12V have thinner plates and much lower resitance, even the marine ones that do 6V.

I spent time talking in person to a Trojan Technical support person on 6V vs. 12V. One statement he made was that load is one of the most important considerations. For people running inverter loads over 100A or so they recomend a Trojan 12V deep discharge bank for the higher load currents. For lower current draws (30-50A) , and dry campers who need deep discharge, the 6V have very high cycle life even discharged to 20-30%SOC. He said, once below 20%SOC, life drops quickly.

The trojan website has lots of information for 12V and 6V deep discharge batteries including cycle life, load current etc.

Which battery (6V or 12V) best works for you really depends on what your needs are and how you intend to use them.