We have had a problem with a small drain on our batteries while "The Mary Rose" (our 1998 30' Excella) is inactive with the cutoff switch in the off position. Methinks it might be the propane leak detector being hardwired to the 12v
system. Anyhow, we bought a small solar "battery minder" from Camping World for about $25. I can't remember what it was called, but the CW catalog shows it sitting on a car dash, plugged into the cigarette lighter socket. I connected it to the battery terminals and even after a couple of months of sitting idle, the batteries are always at 100% when we head out. IMHO, a good investment!