Please help, 87Si with battery or wiring trouble

Ok, so heres the deal. My 87Si prelude was running absolutly fine, no trouble starting or anything (it would turn a couple time to start, but always started up well). 2 weeks ago I got rear ended at a light. No major damage except the bumper was knocked out or whack and cracked and the light is crooked. About 5 days later I pulled into a park for dinner and turned it off and was listening to the stereo for about 15 minutes (I also left my lights on by accident). For some reason I pressed down on the brake pedal and that killed the stereo(which had been totally fine up till then). I tried to start it but it was flat. Ever since then every time I turn it off it runs the battery flat. Do you think this is a problem with crossed wiring(from the accident), or the alternator? Or the battery? It runs totally fine once you start it, but drains once it's off. ANY help would be greatly appreciated. Thanks, Benjamin

make sure your brake, dome, trunk or other lights aren't sticking on, and as always the battery could have an attitude. disconnect the battery overnight and see if it will crank the next morning.

Hey, thanks for the reply. I've done an external check on the car and no lights are on, I also took the bulb out of the trunk light just to make sure. Tonight I pulled in to park and turned it off, then I realised my windows weren't closing, it had already drained or short curcuited. So it only takes a couple seconds, so it's not the battery right? It would last at least a couple minutes if it was that. I'll try disconnecting the battery tommorrow night though just incase.