1999 Chevy Suburban batttery keeps dying

Electrical problem
1999 Chevy Suburban Two Wheel Drive Automatic

im not exactly sure what the engine size is sorry but maybe u can still help me. Ok I have a 1999 suburban, it is equipped with an expensive stereo system that currently does not work it went out about a year ago and I havent fixed it, ok I replaced the entire motor, rewired the ignition, replaced starter and most recently bought 2 new batteries and replaced alternator. But my battery keeps dying even after all this, if I charge it, it will run, park it overnight and it will not start the next day. My father is at lost for words he has no idea what it is besides something electrical, can anyone help me? Could it be the stereo system killing my battery, or something else? I need help I have spent so much money already, what else can I do?