Install batmon.app by entering the following commands in the terminal:
sudo apt update sudo apt install batmon.app
Description:
Battery monitor for GNUstep
Battery Monitor is a battery monitor for laptops. It displays the current status of the battery (charge/discharge and energy level) as well as some information about the general health of the cell.
Homepage: http://www.nongnu.org/gap/batmon/
Version: 0.9-1build2
Section: universe/x11