Original website: http://joeyh.name/code/wmbattery/
Wmbattery displays the status of your laptop’s battery in a small icon. This includes if it is plugged in, if the battery is charging, how many minutes of battery life remain, battery life remaining (with both a percentage and a graph), and battery status (high - green, low - yellow, or critical - red).
A newer version may be available in the Window Maker dockapps git repository:
git clone https://repo.or.cz/dockapps.git