An apparatus for simulating a battery is provided. The apparatus includes a power supplying unit, a state regulating unit and an impedance unit. The power supplying unit is coupled to a power terminal of a battery interface and determines whether to provide an operation voltage to the power terminal according to a device voltage provided by the power terminal. The state regulating unit is coupled to the power terminal to provide a impedance regulating signal. The impedance unit is coupled between the power terminal and a ground voltage and is coupled to the state regulating unit to receive the impedance regulating signal. The impedance unit regulates an impedance thereof according to the impedance regulating signal.