Generally, when the battery voltage is low, the battery is charged with high current and relatively high voltage. However, there is a control point, also called protection point. When the battery terminal voltage is higher than these protection values during charging, direct charging should be stopped. The voltage of direct charging protection point is generally the voltage of "overcharge protection point". When charging, the terminal voltage of battery should not be higher than this protection point, otherwise overcharge will be caused and the battery will be damaged.