A charger circuit for use in controlling charge of a battery pack, which includes a charge control switch and a control unit. The charger circuit has at least one power output terminal and one connection terminal for coupling the battery pack. The charge control switch is arranged to selectively provide a power from a power source to the battery pack through the power output terminal. The control unit is coupled to the charge control switch and the connection terminal, and determines whether to turn off the charge control switch according to a signal based on the connection terminal, wherein the signal based on the connection terminal indicates at least one of an over-voltage condition and an over-temperature condition.