Re: House battery capacity?

The most common size of 6V batery is GC2 which is actually smaller than a Group 27. A pair of GC2 batteries (required to get 12V) should give you around 220AH. Four of them (2 in series and then those in parallel with 2 others) should be about 440AH.

If your batteries specify a Cold Cranking Amperage (CCA) or a Marine Cranking Amperage (MCA) they are likely not true deep discharge batteries and will have a shorter life when used as a "house" battery.