An electronic device includes a power transmit port, a first battery unit, a second battery unit, a first voltage-controlled conducting circuit, a first selective conducting circuit, a second voltage-controlled conducting circuit, a second selective conducting circuit and a processing unit. The first and second voltage-controlled conducting circuit connects the corresponding battery unit to the power transmit port in electric when the voltage of the corresponding battery unit is higher than the voltage of the power transmit port. The first selective conducting circuit connects the first battery unit to the power transmit port in electric according to a first turn-on signal. The second selective conducting circuit connects the second battery unit to the power transmit port in electric according to a second turn-on signal. The processing unit generates the first turn-on signal and the second turn-on signal in selective.