From what I know, watch battery level is not stored separately anywhere in Garmin cloud. Unlike battery level for external sensors, which is stored in the cloud and therethically could be retrieved.

As a workaround, you may want regularly downloading .fit files for all activities and extract watch battery level at the end of activity. Limitation - you won't get watch battery level unless you complete an activity; so that workaround would be suitable only for someone who is doing activities regularly (daily?).

Rule is like when it's available in Garmin Connect website, it can be made available as soon as we know the correct URL to fetch the data.

Closing since technically not possible at this moment.

thanks for taking the time but after further research, this doesn't seem possible as discussed here matin/garth#27 .

thanks anyway