Q: Battery dies when the car is parked

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There were four episodes over the past 4 months apparently linked to the same underlying cause. 1. The attendant at the parking garage called me to say that the lights came on. The lights switch was on "auto", as always. The car wouldn't start, when jumped started failed to respond to the gas pedal. Dealer found bad battery and blown fuse. Replaced both. 2,3. Won't start, jumped, dealer found nothing wrong. Happened twice. 4. Won't start after being left for 40 minutes in front of the store (after dark). Lights were DEFINITELY off. Jump started, drove to the dealership. Dealer acknowledged next morning that the battery lost charge overnight, but wasn't able to pinpoint the problem. The car has a keyless start, and it was found in the "half-on" position when I entered the vehicle, navigator was on, although it was definitely off when I left it. It appears that somehow the car "comes on" by itself when parked, turns on power and drains the battery. Any ideas? Ignition switch?

My car has 158000 miles.
My car has an automatic transmission.

If the battery is discharging while the vehicle is "off", and/or where you have commanded all circuits "off", that means that there is a phantom load somewhere in the vehicle electrical system. A contributing factor could be a faulty charging system, so charging system output should be verified to be sure the battery is being properly charged while the car is running. To find phantom loads, an ammeter is placed in series with the battery to determine if there is current flowing when it is not supposed to be flowing. That ammeter is them moved, from circuit to circuit, to determine exactly which circuit has the malfunction. This is referred to as circuit tracing and if indeed the problem is an electrical malfunction, and in particular stems from power being drawn after you have commanded a circuit or circuits off, this circuit tracing will pinpoint the fault. If you need the assistance of a Mechanic to get this resolved, right at your location, please request an electrical problems diagnostic and the responding certified mechanic will get this issue resolved. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.

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