I don't know what battery monitor tray app most pups and *dogs are using these days. I think some pups are using powerapplet_tray version 2.6, 2.7, and I saw a post somewhere there is a 2.8.
Anyway, it uses a Linux kernel feature that has been deprecated for a long time, and in the 5.10.x kernels that I am using in EasyOS Denfell-series, that feature has been removed.
Have fixed the source, but kept backwards-compatibility. Now version 3.0. More explanation, with link to the source and a binary:
https://bkhome.org/news/202110/powerapp ... rnels.html
If you try it, let me know if it works. It displays information when mouse-over and also when click on the icon.
The binary was compiled with glibc 2.33, but I tested on a Debian-Buster build of EasyOS and it still works with the older glibc.