I have been having this problem with my battery draining for some time. I did manage to trace it back to the battery charge wire on the alternator. I just replaced this alternator and it can't even have 20 miles on it. Is there any parts inside that could be bad that would cause this battery drain? If so can they be replaced without replacing the whole alternator?
I have a new alternator that I haven't installed, but the instructions point out numerous times that if you have electrical problems they need to be fixed first, before installing the new alternator. Easier said than done no doubt, but worth considering. If you have the old alternator maybe you should have it tested.
It appears my car eats batteries. At higher speeds it overcharges. Otherwise it appears to work fine.
It sounds like you have a similar problem. How do you know it's the alternator draining the battery? It sounds like things aren't hooked up right. What about the electrical system is non-stock, damaged, or decayed? I went to Walmart to get a battery once. They insisted on doing a battery and charging system test first. It turned out both were fine. (This was on the other car). They didn't charge me anything for this. Maybe you should go just for the test to see what's actually happening.
I diagnosed the problem by connecting a test light between the negative battery terminal and negative post of the battery. when the light is connected the test light lights up showing that there is a ground somewhere in a circuit. I pulled the fuses one at a time to see what circuit the ground is in. Finally when i pulled the battery charge wire off the alternator the light went out. Pretty sure now that I'm getting a ground thru the alternator. A mechanic friend told me that my regulated was bad.