Battery driven display device includes a battery, first and second comparators, non-volatile memory, controller driven by the voltage of the battery, and display device. Non-volatile memory stores the first and second reference voltages of the first and second comparators measured by using stabilized power supply. Controller detects when the first and second reference voltages of the first and second comparators become lower than the voltage of the battery when battery is connected, and determines the time at which end-point voltage of the battery will be reached based on the first and second detection times at the time of measurement and the measured reference voltages.