A charger includes a first connection port, a second connection port, a DC-DC converter, a first microcontroller, and a second microcontroller. The DC-DC converter is configured to convert a first DC voltage into a second DC current/voltage according to a regulation signal, and output the second DC current/voltage through the second connection port. The second DC voltage is lower than the first DC voltage. The first microcontroller is configured to communicate with a DC charging station by handshake via the first connection port. When the handshake between the first microcontroller and the DC charging station succeeds, the first microcontroller generates a regulation indication according to a result of the handshake between the first microcontroller and a battery, the second microcontroller generates the regulation signal according to the regulation indication, and the first DC voltage is supplied by the DC charging station.