[BassGolf]

Yes, having the stereo live all the time will drain the battery. I had the same situation some years ago, and it wasn't a problem if I drove the car every day; it was when I started going on business trips for a week at a time and came back to a dead battery at the airport parking facility that I realized I needed to do something.

I built a little relay module that provides power to the stereo when I insert the key and cuts power off when I remove it. Give me a couple days to draw up the schematic and post it.