Hi,

FWIW I was also interested in battery level of my Bose QC35 and
checked this some time ago. That time I only checked the low
energy stuff, since the Android application seems to know the
battery status with only LE being connected.

Marcel Holtman wrote:
>> This headset do have dual mode, I searched around using gatttool ant the
>> gatt specification but I find nothing about Battery Level
>> (org.bluetooth.characteristic.battery_level.xml) or Battery Service
>> (org.bluetooth.service.battery_service.xml).

Bose QC35 does not expose battery status through standard battery_level
characteristic. There is a proprietary primary service 0xfebe (which
is assigned to Bose) with a couple of custom services. I assume battery
level can be read through them, but the required commands are unknown.

>> How could I read what's in the Apple HFP extensions?
>
> Start with this one. It describes the extra HFP AT commands that iOS uses:
>
> https://developer.apple.com/hardwaredrivers/BluetoothDesignGuidelines.pdf

Thanks for the documentation link! That is actually implemented for
the Bose QC35. Here is a quick hack providing battery status info
in pulseaudio log:

https://github.com/sre/pulseaudio/commit/d66b66d20e9bc73e6d0ca89283cf2b5675304b00

-- Sebastian