Sounds Crazy Huh ?
3 Answers
First, it's possible that an alternator is bad out of the box, it happens. Then cables may not be good, especially the ground to block or chassis, wherever it grounds, Then if it drains overnight you may have a parasitic drain. See: https://www.youtube.com/watch?v=KF1gijj03_0
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Do I have to pay for a parasitic test ?
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Yup, at a shop you will. They don't work for nothing and you will have to leave the car overnight at least
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