Abstract: A battery capacity predicting method predicts a remaining capacity of a battery unit including a plurality of battery cells connected in series in an apparatus which uses the battery unit. The battery capacity predicting method includes the steps of comparing output voltages of each of the battery cells, and predicting the remaining capacity of the battery unit based on at least one of a minimum voltage and a maximum voltage out of the compared output voltages of the battery cells.

Abstract: A DC/DC converter includes a control unit for outputting a control signal on the basis of a voltage difference between a DC output voltage and a reference voltage; a switching element which is connected to a line of the DC input voltage, and which becomes ON-state or OFF-state in accordance with the control signal; and a minimum ON-state duration setting unit, e.g., a monostable multivibrator, which defines the minimum ON-state duration of the switching element, when a necessary output electric power is low. Preferably, the converter includes a charge-pumping circuit having two diodes and two capacitors, so as to obtain from one capacitor a driving voltage source for driving an N-channel type field-effect transistor as the switching element.