Residual charge in a battery is measured based on a discharge voltage from the battery. A device for measuring the residual charge in the battery includes a fluctuation width amplifier configured to amplify a fluctuation width of a discharge voltage from the battery in excess of a threshold voltage. The device includes a display module configured to display the discharge voltage amplified by the fluctuation width amplifier. The discharge voltage amplified by the fluctuation width amplifier corresponds to the residual charge in the battery. The residual charge in the battery may be determined based on the discharge voltage and the application load data due to an operative application program.