I used to joke as follows.
Why two six volt in series instead of one big 12 volt? (Size 8-d)
the joke is this: You put two six volt in series you get 12 volts at 230 amp hours
You try to pick up a 12 volt 230 amp hour battery you get... A hernia.
NOT that a pair of Group 31's would put you in the same (260 AH) Ball park.
So this argues for multiple batteries in series.
As for GC-2/G-31.. GC-2 generally cost less and are TRUE DEEP CYCLE
G-31, generally cost more and though you can get 'em in Deep cycle, most you find are not.
Oh, and yes, I can pick up an 8-D safely and carry it without injury, or two G-31's at the same time.. However I know many that can not.
