Originally Posted by CaptTom
Agreed. The advantages to the 6V GC batteries are high AH rating for their size and cost, full deep-cycle capability, a smaller footprint that gives you some mounting flexibility, and an easier job installing and removing them. Sam's club also sells GC batteries, as does Batteries Plus.
I agree you would do fine with a conventional 12V battery, but at least spec out a pair of GC batteries, you may find that works better for you.
They do have lots of Ah's but of course it takes two before you can compare those Ah's to a 12V battery. In terms of energy density by weight you can compare two 60lb batteries on Deka's website:
21.35 Wh/lb for the Group 31 (59 lbs, 105ah)
21.32 Wh/lb for the Golf Cart GC10 (60.5 lbs, 215ah)
Basically a rounding error in terms of the difference. I've run the numbers on density by volume and again it comes out the same. So there may be advantages for the GC's but it's not density.