The reading for Vbatt is dependent on the +5 voltage readings?

Forking the discussion from:
Automagic low-battery shutdown for Charlie?

Apparently the micro-controller processor chip is an ATSAMC20J - which is a 32 bit microcontroller with some serious chops!

This is the feature overview from the datasheet:

Damn!  That would be sweet on a broken-out dev board like an Arduino!

I am going to read more and find out what is going on.