1996 Ford Explorer battery drainage

I would leave my explorer sit for a few days at a time and when I would want to drive it, the battery would be completely drained. I would charge it back up for a few hours, and still do the same thing. So I went out and bought a new battery. That wasnt the problem. So then I took the alternator out and took it to advance auto parts and they said that the alternator was fine. I put the alternator back in and checked for anything thats staying on while the car is off with a volt meter. The rear defroster read 10-12 volts and the dealership said that there should be no power from that source when the vehicle is off so I took the fuse out. The battery is still draining. I dont know what else to do or think of. Thats why im asking you and hopefully you can come up with a solution. Thanks. Rob