My Apple Watch shows 10% battery and dies but as soon as I plug it in, it shows 64%. But then if I take it off the charger it happens again immediately

Hi

As your Apple Watch's battery level indicator is not behaving as expected, your watch may require service.

Before contacting Apple, it may help to follow these steps, which have previously resolved battery-related issues for other users, including after software updates, when usage has not otherwise changed (check after each):

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

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

Close certain apps and then restart (normally) both your iPhone and your Apple Watch:

• If an app unexpectedly quits, stops responding, or won’t open - Apple Support
  • Close the Watch app (if open) on your iPhone.
  • Close any apps that you may have noticed are not behaving as expected on your Apple Watch.
• Turn both devices off together, then restart your iPhone first:
  • Restart your iPhone, iPad, or iPod touch - Apple Support
  • Restart your Apple Watch - Apple Support

If you have ever (not necessarily recently) previously used the Workout app and/or any third-party fitness, sleep or heart rate tracking apps on your watch, then check on your Apple Watch to see whether there is an active or paused session within any of them.

• If there is, then end that session from within the app on your watch (not your iPhone).

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

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

Some users have previously experienced battery life issues in connection with using corporate profiles and/or Exchange Calendars. If you are using an Exchange Calendar, one or more of these steps may help:

• Archive your Exchange Calendar for all items before today.
• Remove / delete all old inbox messages relating to calendar invites (accept and decline notifications).
• Create a rule in your Outlook Mail account that moves all future accept and decline replies, immediately upon receipt, into a separate mail folder that does not sync with your iPhone and Apple Watch.
• Check your Exchange Calendar for errors.

Test by changing notification settings and/or by removing watch face complications and third-party apps:

• Turn off notifications for third-party apps and test performance after re-enabling them one at a time:
  • On your iPhone, in the Watch app, go to: My Watch (tab) > Notifications.
  • See and respond to notifications
• Remove watch face complications and monitor performance as you add them back:
  • Change the watch face on your Apple Watch - Apple Support
• Remove third-party apps from the Dock and/or remove them completely from your Apple Watch and then monitor performance after adding them back, one at a time.
  • Use the Dock on your Apple Watch - Apple Support
  • Use apps on your Apple Watch - Apple Support
  • Open apps

If the issue persists, then I suggest that you contact Apple Support (remote diagnostics and/or mail-in service may be available, if required), make a Genius Bar reservation or visit an Apple Authorised Service Provider for assistance:

• US: Apple Watch Service Answer Center - Apple Support
• Elsewhere: Select your country for Apple Watch service and repair information

More information:

Apple Watch - Battery - Apple

Batteries - Maximizing Performance - Apple