Check battery level of connected bluetooth device on linux

This might be a bit late to the party but for me this Python project has worked fine:

https://github.com/TheWeirdDev/Bluetooth_Headset_Battery_Level

I only had to change the port in line 57 to 3 for my no-name X5 headset. If it hangs or errors with "connection refused" try a different port.

The Python program uses AT commands via RFCOMM and should work while Pulseaudio is using the A2DP sink (mine reconnects). Python 3 is needed as 2 doesn't have BT-Serial sockets. Windows will probably not work as it lacks bluez. It basically does the same thing as the Pulseaudio hack here: https://stackoverflow.com/a/56390625/920122

If you want to look at the commands as they are exchanged, try my debug fork: https://github.com/clst/Bluetooth_Headset_Battery_Level

For me running this in terminal worked:

upower --dump