Ordinary personal computers have a power supply that converts 120AC to 12DC, but they are limited to the amount of current that is designed into a PC, and not the current consumed by electric motors or other higher-amp devices. If you go with your #10AWG idea, be sure and put a fuse or circuit breaker near the battery positive end. It would be easy, and dangerous, to accidentally drop a hot lead onto something combustible. I like the other tips suggested.