Electrical issues can be the worst, maybe more so than mechanical ones because of the unknowns and having to trace wires back to buried harnesses. Check for lights left on in places you don't normally go into (i.e. Glovebox light, under hood light, etc.). You could pull fuses in areas that are suspect - someone had posed this idea with the radio fuse. Until you get it rectified you can get one of those $5 manual battery shutoff switches. They allow you to isolate the power to the battery when parked. I use them on several of my older vehicles during winter storage periods to keep the battery fresh and to prevent any parasitic draw. They are on eBay and some of the local parts stores stock them too. I wish you luck!
