I think I found one of the reasons we may have battery drain . If on your watch move on widgets you will see the % and days or hours left. While you have your Garmin connect app on your phone open , go to watch and go to activity. Click on your activity to change the settings and then you will see on your watch the remaining time to go from days to hours. Practically your phone app , open in the background the watch activity and activate GPS etc. so if you don’t move from the activity settings on your phone app, the watch will keep all the activity sensors open and this will drain the battery.