My brother in-law has a 97 F-150 2wd that will start and run once the battery is charged, but then after about 15 minutes of being shut off it won't start back up. He replaced the battery and tested the alternator on the truck at autozone. The guy there said the alternator was good and functioning properly, and he has ran the truck without even having the battery connected. We also checked the current between the positive battery terminal and the negative clamp which we disconnected from the battery. It was zero as it should be, indicating there isn't a short circuit, which was my first thought. Any suggestions on what could drain the battery that quickly?? He started the truck only twice after he bought the new battery and it was dead.

 

It's possible that the new battery isn't any good. I would get it tested again to be sure.
Otherwise if there is a big enough draw to kill the battery in that short of a time you should have quite a bit of current flow between the battery and the disconnected terminal. It would be enough of a draw that you'd get a pretty good spark when you connect or disconnect the battery.