The invention provides an electronic device and system for DC voltage conversion. The electronic device (100) includes: a first input terminal (102) to which a first DC supply voltage of a fuel cell system (200) having a controllable supply voltage is provided; a second input terminal (104) to which a second DC supply voltage of a rechargeable secondary battery is provided; a DC voltage conversion circuit (110) which receives the first and second DC supply voltages from the first and second input terminals, and supplies a current of a desired voltage to a load; a charging circuit (120) which receives the first DC supply voltage from the first input terminal, and supplies a DC supply voltage for charging to the second input terminal; and a control circuit (140) which determines a desired value of the first DC supply voltage in accordance with a value of the second DC supply voltage of the secondary battery, and provides the determined desired value to the fuel cell system.