Detecting that a battery is inside a dock?

[Bastien Nocera <hadess@hadess.net>]

Hey,

I have access to a convertible Toshiba machine where the 2nd battery 
is in detachable keyboard. This is the decompiled DSDT:
https://hadess.fedorapeople.org/toshiba.dsl

There's no BAT0, BAT1 is in the screen, and BAT2 is in the keyboard.

BAT2 can be ejected (it has an _EJD method), but the dock code doesn't 
see it as having a battery:
$ pwd
/sys/devices/platform/dock.0
$ cat flags
16
$ cat type
dock_station

Any ideas what might be missing here?

I'd eventually like to be able to say that, if I can detect that the 
battery is inside the dock, to mark it as such in the UI[1] (even 
better would be to say it's "in the keyboard" but I'm not sure we can 
easily detect that).

[1]: https://bugzilla.gnome.org/show_bug.cgi?id=748592