I bought a used alumminum fishing boat and it came with a trolling motor and battery. I took it out and it ran great. We used it for awhile fishing and it started to die. I plugged it in to my charger when I got home and it said it was charging. I hooked it back up to the trolling motor and now the trolling motor won't work at all. Is the battery dead, or is it the charger? Thanks.