Abstract: The present invention discloses a charging device electrically connected to an external power supply and a rechargeable battery pack, so as to perform a charging procedure of the rechargeable battery pack. The charging device includes a detecting module, a processing module and a charging module, wherein the processing module is electrically connected to the detecting module and the charging module. The detecting module is used for detecting both the state of charge of the rechargeable battery pack during the charging procedure and a polarization voltage corresponding to the internal resistance of the rechargeable battery pack at different states of charge. The processing module generates a current adjusting parameter according to the polarization voltage and the state of charge. The charging module receives the external power supply and adjusts the charging current outputted to the rechargeable battery pack according to the state of charge and the current adjusting parameter.