Install wmacpi by entering the following commands in the terminal:
sudo apt update sudo apt install wmacpi
Description:
ACPI battery monitor for WindowMaker
This is a battery monitor that uses ACPI to query the battery status. This version should work with all recent kernels (vanilla > 2.4.21), both 2.4.x and 2.6.x.
Homepage: http://windowmaker.org/dockapps/?name=wmacpi
Version: 2.3-2build1
Section: universe/x11