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Q: Can a bad alternator drain a battery

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My car hasn't been driven in 2yrs. I bought a new battery and it was cranking. Two days later, I try to crank it and the battery is dead. Will a bad alternator drain a battery

My car has 150000 miles.
My car has an automatic transmission.

Hi there. Generally, a bad alternator will not drain a battery, but will not maintain the battery charge. It sounds like you have a parasitic draw on the electrical system; something is continuing to power on after the vehicle is turned off. Perform a quick check to see if the glove box light or the trunk light is staying on after closing; this is more common than most people realize. If these are operating ok, then there would need to be a parasitic draw test procedure performed that isolate the circuit, then the component or wire that is causing the draw. I suggest having a qualified technician perform an inspection to avoid replacing unnecessary parts. Your Mechanic has several available technicians that can assist you with a battery is dead inspection.

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