What time frame are we talking about? Days, weeks?
There is a constant parasitic drain for the 'keep alive' circuits, that, over time could kill a battery, ESPECIALLY one that's old and weak.
I think that drain is around 20 ma.
The previous poster talks about the 'retained accessory power' feature that's good for about 10 minutes of accessory use after shutdown (more than just windows). I've never seen this feature to fail as suggested, but YMMV.
I've had this dead battery issue on my seldom driven '88; I just keep a battery tender on it.