according to:
https://forums.garmin.com/developer/connect-iq/f/discussion/255692/wf-limitation-app-battery-consuming
when simple app is running it consumes 5 times more energy than complicated watch face
I've done 2 test
1. remove timer and app only draw 7 times (system called becase of disconnected message) during about 1:20 hour times screen like below
result battery from 56 to 52% -> 4% -> 0,05%/minute (with timer 0,07%/m, watch face 0.014%/m)
2. jogging with gps, df, bt etc -> 0:45 4% -> 0.089%/minute