An apparatus using a battery includes a receiving unit, a determination unit and a calculation unit. The receiving unit receives a dischargeable capacity, a first voltage and a second voltage from the battery. The first voltage is used to display the end of an available time and the second voltage is used to carry out a low power operation. The determination unit determines whether the first voltage is less than the second voltage. The calculation unit corrects the dischargeable capacity and calculates the available time based on the corrected dischargeable capacity, if the determination unit determines that the first voltage is less than the second voltage.