Q4os upgraded from Jessie to Stretch - how to upgrade kernel

[tillea]

Hi,
thanks to the great Q4os developers I now have a quite decent Debian Stretch system running.  After I managed to flash the eMMC with Q4os I simply editet sources.list to point to Stretch instead of Jessie and did a dist-upgrade.   I needed to fiddle a bit with the graphics since X was lost but rebuilding libump and xf86-video-fbturbo under Stretch did the trick.  (I'm a Debian developer and might consider creating at least an official libump package - need to check the license of fbturbo whether it is acceptable in Debian.)
I installed XFCE4 which I prefer over the desktop choice of the Q4os developers.  So far my desktop now looks quite similar to my Intel based laptop. :-)
However, I came across two problems:

1. Xfce4-battery plugin always shows an empty battery even if onscreen notification says "battery full" when plugging in power adapter (I tried do fix this by an acpi dkms kernel module which unfortunately does not build with the current kernel)
   
2. I wanted to use cryptmount which issues an error that lets me assume that loading a certain kernel module is a problem (sorry, I do not have my pinebook at hand to be more precise)
   

So it seems upgrading the kernel would probably cure my both problems.  After a question on the debian-arm mailing list it seems that exactly this would be a problem.  Is there any hint how to get a more recent kernel than the one provided with Q4os 1806 and how can I install it (without just going the Q4os route again - I'd like to save my current installation instead of doing a full Q4os reinstall.
Kind regards, Andreas.