An apparatus for controlling power efficiency of an information processing device is disclosed. The apparatus includes a voltage converter that converts an input voltage into a predetermined output voltage, an information processing device that consumes power supplied by the voltage converter, a battery pack that is charged using power supplied at a predetermined charging voltage by the voltage converter, and a controller that determines the input voltage where the power supplied by the voltage converter exceeds power consumed by the information processing device and a difference between the input voltage and the predetermined charging voltage is minimized. A method and a system also perform various functions of the apparatus.