Bought 2 new batteries for a 2 bank system, then left the boat for a few weeks, with the main switch to "off". Disconnected shore power
as well. Came back to one very dead battery
(9.6V), but the other was still at 12.35V, so it seems that one of the banks was isolated from the problem.
Any really likely culprits? Shouldn't turning the main switch to "off" turn EVERYTHING off? Is something hooked up outside the system, and how to find it?
I'll be back at the boat tonight.