Please add the battery level indication of the devices to the Garmin Connect app, possibly with a setting to customize at which battery level the app sends a low-battery notification.
Interestingly the sensors' battery level can be checked from GCM, but not the Garmin devices'
Note: this is a clone of https://forums.garmin.com/developer/connect-iq/i/bug-reports/feature-request-add-battery-level-to-garmin-connect-app because Garmin recommended to recreate tickets that are still relevant...
Please up-vote if you're also interested, so that Garmin knows I'm not alone ;)