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Q: The car won't start after battery was overcharged. 2001 Hyundai XG300

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I had the battery in my car overcharged by the alternator. It was charging about two hours longer when I stopped it. After waiting for a while, I started it and had the negative cable disconnected. At that point, the AC, dashboard lights and all other interior and exterior lights flashed and the car cut off completely. The battery had 12.8 volts. So, I had the cable replaced along with the 30 amp starter fuse and the 120 amp fusible link. Then, I attempted to start the car again but the car was still completely unresponsive. What happened here? What should I do?

Hello there. It sounds like you have a cloud of things going on with your Hyundai XG300. If the alternator is overcharging the battery, then there is a good chance the alternator has failed. Most of the time, this is caused by a faulty voltage regulator that is internal to the alternator and must be replaced together. Once the alternator has been replaced, the battery should charge at a normal voltage.

If the alternator either over or under charges the battery it often becomes damaged. In many cases, the alternator and battery are replaced together due to the alternator causing the battery to fail. A qualified technician, such as one from YourMechanic, will load test the battery to check its condition and perform any other tests to diagnose this starting issue.

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