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Q: Battery or Charging system problem

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My car died in my driveway yesterday, I went out and checked my fuses and the connections on my battery. The voltage read 8.4. Today I jumpstarted my car and it started right up, the voltage went up to 15.1. Within 15 minutes the car was dead again with 8.2 volts last time I checked. A few minutes ago I went out and checked what kind of battery I have. When I unlocked my car what little power I still have came on. When I opened my hood I could hear the battery making what sounded like a boiling sound. Could my problem be just a bad battery or something with my charging system like the alternator overcharging?

My car has 40701 miles.
My car has an automatic transmission.

This may suggest a failing voltage regulator. The voltage regulator is a unit that regulates the charging of the battery by the alternator. When the voltage regulator is not working properly, this may result in the alternator allowing too much power to be delivered to the battery resulting in damaging wires and prematurely sometimes destroying the battery. A common sign of this is usually the acid inside the battery boiling causing the battery to swell. In other cases it may result in the alternator not supplying enough power to the battery, resulting in undercharging the battery or not charging it at all. I would recommend having an expert from YourMechanic come to your location to diagnose your vehicle’s charging system.

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