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Q: Charging system failure.

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The battery drained 2 weeks ago because I left the lights on. Now whenever I drive, the battery always drops and the RPM stays lower than usual. Just recently it stopped going as if the battery drained again. and now the service engine soon light is on constantly.

My car has 8299 miles.
My car has an automatic transmission.

This may be a sign of a weak battery, a failing voltage regulator or failing alternator. As you may know, the alternator is responsible for charging the battery while the engine runs by generating amperage and recharging the battery while the engine turns the alternator. The voltage regulator is a unit that regulates the charging of the battery by the alternator and maintaining a certain amperage while the engine runs. When the alternator is not working properly, this may result in the battery quickly losing charge and the car losing all power as you have described. You may also notice a whining sound as a result of the bearings inside the alternator begin to fail. I would recommend having an expert from YourMechanic come to your location to diagnose and repair your charging system.

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