Chosen Solution
it is a parasitic battery drain. i think it might be caused by the radio drawing too much power after the car is off.
rcs1055 , That could be a possibility especially if aftermarket radio install, you could remove fuses or unplug the radio/amp and see if battery drain stops using a DVOM. Use the 1st link below to see how to test for parasitic draw and a couple links for radio removal so you can unplug and check wiring,etc. Good luck. I hope this helped you out, if so let me know by pressing the helpful button. https://www.youtube.com/watch?v=KF1gijj0… https://www.youtube.com/watch?v=wQj_MB2-… http://www.corvettemagazine.com/tech-art…
Well if that didnt work id be looking at the alternator …there are somethings inside i dont recall proper term ( rectifiers?) but when they go bad they will drain your battery overnight or maybe if it sits a couple days….. i have had many late model gm cars do this so if all else fails its free to look into it
