First

The project use a wrong way to get battery level(Headphone/Headset)
I try to get Bluetooh headphone battery level by BLE GattService, but this is not a good idea.

For headphone/headset

Headphone/Headset can use HFP to report battery level to ios.We should use hfp to get headset's battery level.
Apple extend HFP command, help headset report a headset state change:

• Request: AT+XAPL=[vendorID]-[productID]-[version],[features]
• Response: AT+IPHONEACCEV=[Number of key/value pairs ],[key1 ],[val1 ],[key2 ],[val2 ],...

Unfortunately, microsoft no provide api. You have to code Bluetooth Driver to supersed Microsoft Driver.

BluetoothLEBatteryMonitor

Windows BluetoothLE Battery Monitor
Version 2.0

Note

Use Universal Windows Platform (UWP) Windows Runtime API at Windows Forms

TODO

• BEL feat: Replace timer loop to get BatteryLevel with event listener

References

• https://github.com/joric/bluetooth-battery-monitor
• https://github.com/sensboston/BLEConsole