A device is used for measuring an output voltage of a battery. The device includes a detecting circuit, an encoding circuit, a control circuit, and a processing circuit. The detecting circuit is configured for detecting the output voltage of the battery and generating a first signal, a second signal, and a third signal accordingly. The encoding circuit is configured for generating a first code and a second code according to the first signal and the second signal. The control unit is configured for modifying the second code when the third signal indicates that the output voltage is lower than a predetermined value. The processing unit is configured for generating and outputting display control signals according to the first and second codes. The display control signals are used to control a display panel to display information of the output voltage of the battery.