Originally Posted by jkoebel

GP relay might be screwed up causing a constant train?

Disconnect GP relay entirely from battery supply. Try and see what happens jumping/starting the car. Go for a good drive, then let it sit over night.

Draining a battery dead-dead is a good way to kill them though, they're not designed for that. (Deep Cycle batteries, which ours are not, can be drained in that way.)