I guess my dead battery was a fluke. I accidentally left a dome light on last night, and because I level 2 charged instead of level 1, the 12 volt battery had to keep power to the light nearly all night
. The car didn't have any problems starting, though.
I'm still saying that the radio got stuck in a half-powered state when my battery went dead a few weeks ago. The car was started, moved, then shut back off, so the radio didn't have time to fully boot up (aftermarket Android Head unit) and thus drained the battery over two days.