My SVX eats batterys

[svxsubaru1]

This is the theird, or forth battery my SVX has gone through in about 2 months. I have a 5spd SVX, and it seems like my alternator is not getting a charge to the battery. When ever i put a new battery in, or charge one up it only last about 2- 3 days before its complety dead, one time the battery was so dead that i had to drive home by pooping the clutch to get it to start. I drove for probley 10-15 mins on a complety dead battery so i know that the alternator works. I upgarged the grounging for 8 gauge to 2 gauge and i thought that fixed it, but no it jsut killed abnother battery. When ever my battery is about dead all the idiot lights come up very dimmley and fade away every so often. Any ideas what would casue this?