1996 Chrysler Town and Country New battery slowly drains wh

Electrical problem
1996 Chrysler Town and Country 6 cyl Front Wheel Drive Automatic

After getting stranded on the side of the road, we assumed the alternator had gone bad. We removed it and had it tested at an auto parts store, and it passed. So we put it back in, and tested the battery. It failed, so we replaced the battery and it seemed to work well, for a few hours. While driving it, the battery light came on, but it didn't seem to be dropping much in voltage. The next morning, we left it idling, and went outside to find it dying.

Essentially, brand new battery, good alternator (according to a professional anyways), wiring is good, no blown fuses/short circuits that we can find, and a failing electrical system. At the auto parts store we were told that this particular model has the voltage regulated by the computer, and that the computer may be the problem. Basically just wondering if that's likely, or if we need to be looking elsewhere. Thanks.