A multi battery power system includes an electronic device and an extension dock. The electronic device includes a first power storage module, a first connector, a second connector and a power conversion module. The first power storage module includes a first power storage unit. The first connector is coupled to the first power storage module. The power conversion module is coupled between the first power storage unit and the second connector, and converts power stored in the first power storage unit into a converted output voltage and transmits the converted output voltage to the second connector. The extension dock includes a third connector and an electrical load. The third connector is paired with and selectively connected to the second connector of the electronic device. The electrical load is coupled to the third connector, and selectively receives the converted output voltage from the electronic device via the third connector.