So, consolidating all of my research here and venting since i never got any feedback from Garmin even after sending them all of the diagnostics they requested i send to them.
short story, i'm 99% sure culprit of my problem is Garmin Connect:
- GC version 4.9
- Forerunner 935, FW9.70
- iPhone 7, IOS 11.4.1
basic problem:
GC while supposedly running in the background, is killing my iPhone battery. this did not happen prior to GC 4.7 (released in late May 2018), and it has affected my iPhone and watch with other version of iOS and FW and it is exactly traced to the upgraded to GC4.7. i wish i could role back to that old version...
when i look at the Battery Usage stats on my iPhone, unless i disconnect my watch (using hotkey) or force quit the GC app, my "Usage" and "Standby" numbers are identical. and if i look at GC in particular, and let it operate that way for X horus or days, it is running in the background 100% of the time. again, this did not happen prior to GC 4.7.
kludgy fix: if i force quit the GC app on my iPhone, the problem goes away. i don't get a notification counter available on my phone, but i can actually see notifications via the Garmin Notification widget if i look at the list that's there. this isn't a super bad solution, but it seems crazy that i have to force quit GC whenever i use it, and moreover, i can't use the watch the way it is designed to be used unless i am willing to have it eat 25-30% of my phone battery over the course of the day.
no solutions except waiting for Garmin to fix GC?:
i have done everything including: wiping my watch clean and not installing any widgets/apps/watch faces; resetting my phone to scratch; reinstalling GC... all of these don't solve the problem.
Garmin: Please fix this!