How to show bluetooth headphone battery in macos? Hovering over the device doesn't show the battery level.
When connected to the iPhone, I was able to get the battery level in the widgets screen.



How do I know when I have to charge the headphones?
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