The voltage generated by the generator changes with the speed of the car, the speed is higher than the battery voltage, the maximum is more than 30% of the battery voltage, the speed is lower than the battery voltage, and the minimum is no voltage.
The car has a voltage regulator (regulator), the role is to reduce the high voltage of the generator to a certain range for the car to use, while charging the battery; When the generator is low, the voltage regulator automatically draws out the current of the battery, and always ensures that the car has a stable voltage power supply.
If your voltage regulator is good, no matter how high the engine's voltage is, it will automatically adjust to the range where the battery can float from charge for a long time, and there is no need to worry about overcharging.
The voltage regulator is such that it automatically adjusts the charging current, the charging current is large when the battery is short of power, and it is automatically reduced to the current that can be charged for a long time after sufficient.