1999 Isuzu Rodeo eating batteries

Ok, here's the deal. I went to start my car two days ago and it wouldnt crank. Dead battery I figured, so i got jumped off, drove to where i wanted to be, cut it off and left. A few hours later I return, jump it off again and the car dies before i can leave the parking lot. So, I hitched a ride to the store and got a new battery. Replaced the old one, drove home without a problem. Next day drove just fine as well. This morning I get in my car to leave for work, and it wont crank. I figure it has to be a short somewhere in the system but I am looking for help anywhere I can find it. Anyone have this problem before or know how to fix it? Also and tips on locating a short would be helpful. Thanks

maybe it's the alternator.

Is there any way to test for the alternator? I tried testing by cranking the car and disconnecting the negative battery terminal. The car kept running but is that a valid way to test the alternator?

You can have the alt load tested.

Do you have any aftermarket stereo equipment?

Yes, I have an aftermarket head unit.

Is it a recent install? Did you cut out the factory harness or do a clean install with a univerisal plug and plug harness?

how many miles on the current alt?

The radios been in there for 5 or 6 months, clean install. The alternator has no more than 30,000 miles on it

I'd take it in to a shop to get looked at. There is a possibility that it is the alternator, but it could be a host of other things.

Ok, so the alt has been replaced once? If so Isuzu are very hard on aftermarket alts.