The program contains a C++ console application showing all connected XInput Controllers (e.g. Xbox 360 or Xbox One controller) and their battery status. A GUI, written in C#, displays the battery level of the controller of your choice in a tray icon. The GUI refreshes every ten seconds.
If you do not like the design of the icons, you can simply replace them by your own version.
The C++ programm uses the Xinput 1.4, so it should work fine with Windows 8, 8.1 and 10.