MacOS – How to show bluetooth headphone battery in macos

I hate to have to answer in the negative but the answer is: you can't.

I've done a lot of searching the web, testing utilities, playing with ioreg on the commandline, scrutinizing System Profile reports, and it appears to me that OS X has no way of displaying battery level of connected devices that don't automatically display battery status in their Bluetooth menu Device submenu, even if iOS devices display detailed level info for the same Bluetooth device when connected to them. OS X just appears to completely ignore this capability in all but a few default (Apple-manufactured, it appears to me) devices.

On my iMac(macOS 10.12.6), none of solutions mentioned above works. After reading the man page of ioreg. The solution that works on my computer is:

// the -r option is used to reduce output
// the -l option is used to display properties for all object
// by default some object properties are not shown
// the -c specify device class, the class could be specific or general
ioreg -c AppleDeviceManagementHIDEventService -r -l
ioreg -c AppleDeviceManagementHIDEventService -r -l | grep -i battery

// instead of using device io class, you could also use a property key to query
// you need to know one of target device's property key(-k), for example it is BatteryPercent for Bluetooth keyboard and mouse
// any device with this property will be listed
ioreg -r -l -k "BatteryPercent"
ioreg -r -l -k "BatteryPercent" | grep -i battery

There are some other device classes to try for the -c argument: AppleHSBluetoothDevice AppleHSBluetoothHIDDriver AppleMultitouchMouseHIDEventDriver AppleHIDKeyboardEventDriverV2, they give different output.