Please listen to what pianotuna is saying, especially about connecting the charging cables.
I used to have a boat and had 6-volt batteries in series for my house bank and 12-volt batteries in parallel for my starting bank. Worked great but for RVing I lean more towards 12-volt deep cycle batteries, instead of 6-volt batteries in series. The reason is because if you have 2 6-volt batteries in series and one cell goes bad, then you have nothing. But if you have 2 12-volt batteries in parallel and one goes bad, you still have one good battery to limp along on.
Tim
