Why does my Apple Watch battery drain so quickly?

Battery life varies depending on use and other factors. Examples are detailed here:

Apple Watch - Battery - Apple

Apple's tips for maximising battery life on Apple Watch are detailed here:

Batteries - Maximizing Performance - Apple

If your Apple Watch is experiencing significantly shorter battery life than Apple's examples suggest that you should expect, then it may help to follow these steps, which have previously resolved battery life issues for other users, including after software updates when usage has not otherwise changed (check after each):

If you have not yet done so, update your iPhone and Apple Watch to the latest software, starting with your iPhone:

• Update the iOS on your iPhone, iPad, or iPod touch - Apple Support
• Update your Apple Watch - Apple Support

Restart both your iPhone and your Apple Watch, turning both off together and then restarting your iPhone first:

• Restart your iPhone, iPad, or iPod touch - Apple Support
• Restart your Apple Watch - Apple Support
• If the issue persists, next close open apps on your iPhone and then restart both devices again.

If you have ever (not necessarily recently) previously used the Workout app and/or any third-party fitness or sleep tracking apps to record workouts on your watch, check on your watch to see whether there is a paused activity within any of them. If there is, end that activity from within the app on your watch (not your iPhone).

• If in doubt, remove any such third-party apps from your Apple Watch.

Unpair and re-pair your Apple Watch:

• The Watch app on your iPhone takes a backup of your watch automatically when unpairing via the app.
  • When setting it up again, initially choose to Restore from Backup. Most data and settings will be restored, with some exceptions (eg Apple Pay cards, passcode).
  • If the issue persists, consider instead unpairing and setting it up as a new watch.
• Unpair your Apple Watch and iPhone - Apple Support
• Set up your Apple Watch - Apple Support