Battery discharges overnight
replaced alternator and battery also tested starter. jump start vehicle and runs fine until it
is parked for the night. serpentine belt is good
You have a short or open circuit somewhere. Check your lights and other electrical components on the inside of your vehicle.
boho is right, if you can't locate it by checking all the components or lights inside, then check out the Video by Ericthecarguy.com on parasitic draw test.
I was recently having this problem as well... I ended up buying a new battery and that solved the issue. It was a 2008 truck with the factory battery.
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