The principle of the lithium battery 26 charging port is voltage limit constant current, which is controlled by the C chip. The typical charging method is: first detect the voltage of the battery to be charged, if the voltage is lower than 3V, precharge first, the charging current is 1\/10 of the set current, and after the voltage rises to 3V, enter the standard charging process. The standard charging process is: to set the current and voltage as parameters, through the C chip control, the lithium-ion battery is charged with constant current and constant voltage.