Charged it. Rode about 1.7 hr. Powered it off, not standby. Three days later I turned it on to ride, it indicated zero and died after a few minutes. Someone else reported this but I couldn't find the thread.
I'm pretty sure the 820 doesn't have a magnetic compass sensor. What you're enabling is screen that displays direction of travel based on changing GPS position, not magnetic heading. So enabling or disabling it is not turning on or off a piece of hardware that would drain the battery. That doesn't mean that enabling the compass doesn't do something else that affects battery drain.
Many phones do have a magnetic compass, but the 820 doesn't.
I'm the poster that originated this thread. I only had that one instance of battery drain while the unit was off and haven't experienced it since. My 820 is at 8.5 as I haven't yet updated to 8.7.
