A charging device for direct-current, hereafter referred to as DC, charging of an electric vehicle, comprising: a battery module slot for arranging a battery module therein; the battery module which is removably arranged in the battery module slot and electrically connected to the battery module slot and outputs a voltage to a first DCDC converter; the first DCDC converter for converting the output voltage of the battery module into a first charging voltage; and a charging controller for controlling the first DCDC converter to output the first charging voltage and a first charging current for charging a vehicle to be charged, characterized in that the charging device further comprises a second DCDC converter which is connected to the battery module and the charging controller and is configured to be capable of supplying power to the battery management system, hereafter referred to as BMS, of the traction battery of the vehicle to be charged or charge an auxiliary vehicle-mounted power source under the control of the charging controller, the second DCDC converter having two operating modes: a constant voltage power supply mode and a constant current charging mode, wherein in the constant voltage power supply mode, the second DCDC converter is configured to receive a constant voltage and current limiting instruction sent by the charging controller, enter a closed voltage loop and convert the output voltage of the battery module into a BMS power supply voltage capable of supplying power to the BMS of the traction battery at a constant voltage; and in the constant current charging mode, the second DCDC converter is configured to receive the constant voltage and current limiting instruction sent by the charging controller, enter a closed current loop and convert the output voltage of the battery module into a second charging voltage capable of charging the auxiliary vehicle-mounted power source. a battery module slot for arranging a battery module therein; the battery module which is removably arranged in the battery module slot and electrically connected to the battery module slot and outputs a voltage to a first DCDC converter; the first DCDC converter for converting the output voltage of the battery module into a first charging voltage; and a charging controller for controlling the first DCDC converter to output the first charging voltage and a first charging current for charging a vehicle to be charged, characterized in that the charging device further comprises a second DCDC converter which is connected to the battery module and the charging controller and is configured to be capable of supplying power to the battery management system, hereafter referred to as BMS, of the traction battery of the vehicle to be charged or charge an auxiliary vehicle-mounted power source under the control of the charging controller, the second DCDC converter having two operating modes: a constant voltage power supply mode and a constant current charging mode, wherein in the constant voltage power supply mode, the second DCDC converter is configured to receive a constant voltage and current limiting instruction sent by the charging controller, enter a closed voltage loop and convert the output voltage of the battery module into a BMS power supply voltage capable of supplying power to the BMS of the traction battery at a constant voltage; and in the constant current charging mode, the second DCDC converter is configured to receive the constant voltage and current limiting instruction sent by the charging controller, enter a closed current loop and convert the output voltage of the battery module into a second charging voltage capable of charging the auxiliary vehicle-mounted power source.