1999 Ford Expedition starting problem

After a couple of days the battery is drained so that the vehicle will not start. Everything works until I turn the key to start the vehicle and then evrything goes dead. Once I let off the key turning, the lights and radio come back on. Then I will take the cables off the battery for 5 to 10 minutes, reconnect them, and the vehicle will start without a jump or any problems. I'm tossed up between the starter motor solenoid or another item draining the battery while sitting overnight. Thanks for your help?

All connections are good, clean, and tight. I haven't connected the battery in awhile, so it won't drain again. The battery is reading 12.7 right now. Once I connect it and start the truck, the reading is 14.7, which tells me the ALT is charging and working properly. I'm going to hook up the battery and let it drain tonight, and see what the reading are tomorrow. It will most likely be 10.5, like before. Then I will take the cables off and back on 5 minutes later, and it will start the vehicle without a jump. Crazy huh. I'm thinking the starter first peak, or the starter motor solenoid is draining it, but don't want to change it and find out something else is doing it later. Thanks for your help again.

Ok cool thanks. I will look into that page. But I do realize that there is a starting system and a charging system. I feel my problem is in the starting system not the charging system. But I do feel what you are saying. I'm in the Army as a MAINT TECH, but on diesel ENG's. I do appreciate all your help too.