How to show bluetooth headphone battery in macos?
You can write your custom script on these lines
https://romig.dev/blog/mac-os-quirks-bluetooth-device-battery-low/  using ioreg I/O Registry, code for a implementation is available here on Github https://github.com/aromig/scripts/tree/master/check_battery
You can also use plugins like Akku https://github.com/jariz/Akku