[awsnap]

Without getting into some elaborate T/S steps, I'll say this. Most people don't realize that batteries WANT to return to 12.6V. Now, the charge they have behind that is the issue and sometimes they can 'acquire' some of that too. It sounds like a connection or wire is heating up and causing a bad connection for the starter or for charging system. A battery may be the easiest thing for you to try, but I would also look over those two wires.