Ok batteries are rated in amp hours.. To convert to watt hours multiply by 12 for 12 volt stuff and 10 for 120 volt stuff (Stuff the inverter runs) why the difference? Well, that compensates for losses in the inverter..It is not exact. but under 1,000 watts it's close enough.

Now the batteries:

For this I will give the capacity in the C/20 standard, this means how many amp hours if you discharge smoothly over a 20 hour period. So for example on a Group 24 you woudl discharge at 74/20 amnpos or 3.7 amps.

THE FASTER YOU DISCHARGE.. The Faster still the battery runs down and the slower the longer still it lasts.

I still can't remember that dang discover's name.. Begains with P is all I can do.

Group 24 about 73-75 each

Group 27 around 95

Group 29 around 105

Group 31 130

NOTE: THese are usually MARINE/deep cycle batteries.. YOu should not use much more than 1/3 of their capacity

GC-2..(Six volt Golf Car DEEP CYCLE batteries) used in pairs to make 12 volt 220 amp hours give or take 15 depending on the brand and sub model.. Also applies to the 4D and 8D sizes (Only they are 12 volt) if you can get 'em in Deep cycle.

DEEP CYCLE you can use half the power safely,, More than that and they get old much faster.

What's the difference between running down and getting old? Run down.. Recharge.. Get old.> Replace.

So in order to find out how much battery you have, Add 'em up and go for it.

Batteries in SERIES like the pair of GC2 Add voltage

Batteries in PARALLEL.. add amp ahours

Multiple pairs of GC-2.. Treat each pair EXACTLY as you would a single 4D 12 volt... For that is what it is... Electrically.

Many battery questions regarding six volt pairs are swiftly answered if you think of the pair as a single battery.. Examples

Can I replace just one (Can you replace half of a 4D, same answer)

Must they be the same (Age, Make, Size, et-al) Again, can you imagine a single case 4D that is half and half?

See how it answers questions.