a charging regulation circuit having an input terminal coupled to a power supplier, an output terminal coupled to a node N1, and a control terminal coupled to a node N3, wherein the charging regulation circuit outputs a charging current whose amount is regulated based on a first regulation signal at the control terminal;

an operational amplifier having a positive input terminal coupled to a node N2 which is further coupled to the battery, a negative input terminal coupled to a first reference voltage, and an output terminal connected to a node N4 and outputting the first regulation signal at node N4, the operational amplifier outputting a first level of an enabling signal when a battery voltage of the battery is equal to or greater than the first reference voltage;

a first switch unit for connecting a node N6 to either the node N4 or a node N5 according to the enabling signal;

a second switch unit for connecting or disconnecting the node N4 to/from the node N3 according to the enabling signal; and

a comparator having a positive input terminal coupled to the node N2, a negative input terminal coupled to a second reference voltage, and an output terminal coupled to a node N5, the comparator outputting a second level of the enabling signal when the battery voltage is less than the second reference voltage, wherein the second reference voltage is less than the first reference voltage and the second level of the enabling signal is different from the first level of the enabling signal,

wherein the enabling signal is a signal at the node N6, the voltage at the node N2 reflects the battery voltage, and the battery is connected between the node N2 and ground.