So it's been working fine and I've been ignoring it. Parked it on Friday and went to start it this morning. Did the same thing.
Checked the battery right away, it read 11.9V but slowly climbed back up to around 12.15V at which point I tried again and it started right up.
Oh, and there was a little smoke coming from the negative battery terminal.
I think I'm going to get a new battery this week.