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Q: My batteries keep draining down

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My batteries are both good and the alternator is good but my batteries keep running down. It will start sometime and other times the truck will not start.

My car has 116342 miles.
My car has an automatic transmission.

Hi there. Assuming both batteries are good, the alternator is properly charging. This would lead me to believe there is a parasitic draw on the batteries. This draw must be excessive to run down both batteries.

You could attempt to isolate the draw. Disconnect both negative battery terminals, install a test light inline between the negative battery post and battery cable terminal end on one battery. If the test light is brightly lit, then a draw is present.

Remove and reinstall fuse(s) and relay(s) one at a time until test light dims or goes out. Whichever fuse or relay is disconnected, dims, or causes the test light to go out is the circuit drawing on the batteries.

If the short or component drawing cannot be isolated, or you need further help, I recommend having a certified technician, like one from YourMechanic, come to your car’s location to diagnose the battery drain and guide you through repairs.

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