The cause of the car battery voltage being too high may be battery overshoot or a damaged voltage regulator.

Specifically, there are 2 situations:

1. The charging of the car battery is divided into the main charge and the float charge. Generally, the lead-acid battery is to be charged as the main charge for the first time. After reaching the rated voltage, it is changed to the float charge. When the float charge makes the battery voltage rise to about 115% of the rated value, it should be turned off. The charging unit stops charging. If the battery voltage is too high when the battery is first installed, it may be overshoot.

2. If the overvoltage exceeds 15% after the battery is installed and used, it may be that the generator voltage regulator is damaged, causing the charging voltage to continue to be charged after the charging voltage exceeds the specified value, and eventually overvoltage occurs.