The device automatically displays the current battery level when connected to the battery. If the battery voltage falls below the currently displayed LED bar, the highest LED segment turns off. The LED bar display function means that the LED segments turn off as the voltage level decreases after falling below the threshold for the currently illuminated highest LED segment.

When the battery voltage rises above the voltage threshold of the current LED bar during charging, the next LED segment lights up. The charging status is indicated from the first to the current bar. The LED bar display function means that the LED segments light up as the voltage level increases after the voltage exceeds the threshold for the currently illuminated highest LED segment. When the device is disconnected and then reconnected to the battery, it checks the current battery level and displays the corresponding voltage LED bar.