I've downloaded the bionic-mate-pinebook1080p-bspkernel-0.7.30-140.img image, and when adding the battery applet to panel it says running on AC power while the pinebook was unplugged.
I can build images at my own, so in case you believe it is fixed on master or have any fix that I could check, just drop me a note.
And same applies for anything related to mate, as is the desktop I prefer as I'm more used to gnome ones and the new unit comes with a KDE plasma