Having a problem: I have recently replaced the battery and checked my alternator (it checks out good) on my 1996 Subaru legacy 2.5 GT

Run engine without switching any of the items and connect a voltmeter to your battery. It should read more than 13volts. If less than that but reads about 12.5V then check drive belt tension. If it reads OK (above 13V but not exceeding 14.5V) then switch on each item individually to check for biggest voltage drop. The one that creates the biggest drop maybe the one that creates that drain. If drop only happens when ALL items are on. then your alternator may need servicing because it could not cope with large loads. Also check all wires connected to it (alternator).