Q: Activity and Battery Life

Hi

The Activity app runs all the time and cannot be stopped. I think you may mean that you started a Workout using the Workout app (the icon for this is a running person on a green background). That would certainly use more battery as the watch measures heart rate continuously during Workouts.

Stopping a Workout

To stop a Workout that is still running:

• Go to the apps on your Apple Watch by pressing the Digital Crown once.
• Tap on the Workout app.
• Either:
  • Force press on the display to see Pause / End (and tap on End) or
  • Swipe all the way to the left to see Pause / End (and tap on End).

Use the Workout app on Apple Watch - Apple Support

Restarting Apple Watch

After you have checked this, you can also try restarting your Apple Watch, which may help if the problem continues.

Restart: Press and hold the side button until you see the Power Off slider; Drag the slider to turn off completely; Afterwards, press and hold the side button until you see the Apple logo.

Restart your Apple Watch - Apple Support

Tips for maximising battery performance

See also this article: https://www.apple.com/uk/batteries/maximizing-performance/#watch