Just little addition to what Mentalist said - AFAIK device hanging totally instead of rebooting has one disadvantage - possible filesystem corruptions. Watchdogs tends to unmount filesystem before rebooting, just like bme does (#fixme if I'm wrong). .
Anyway, especially this line: cat /sys/class/power_supply/bq27200-0/charge_full_design 0 ...makes me wonder, if Your ID pin of battery is even connected/recognized? That could be source of problems, BUT - (another AFAIK) bme turns device on in < 1 second when unable to probe ID pin. I never heard that R&D mode disables this behavior - can someone running on R&D confirm/deny this? And, wasn't temperature also probed on ID pin?
It's VERY strange all together. could other people, reporting there "same issues" do similar cat probing? I think first of all, we need to check if it's "reproduceable" problem, that may hit some devices, or jvollmann's troubles are unique, and other doesn't share same symptoms. From top of my head i would still say "damaged bq_27200 chip", but somehow voltage and temp is probed correctly... Huge WTF.