using apple watch
Why do the lights stay on on the back of my series 7 watch
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They should only stay on during (and shortly after) a workout. If hey are constantly staying on otherwise it will drain your battery quickly.
The first (and simplest) thing to try if something isn’t working right is to restart your Apple Watch and its paired iPhone. If necessary (device not responding), try a forced restart. Both methods can be found here:
How to restart your Apple Watch - Apple Support
Restart your iPhone - Apple Support
If that doesn't help, the next steps would be to unpair and pair your watch again and restore from the backup just created. This should result in no loss of data. It deletes all temp and corrupted files and re-indexes the file system.
Unpair and erase your Apple Watch - Apple Support
Set up your Apple Watch - Apple Support
Also see the 'Get the most accurate heart rate measurement' section in:
Get the most accurate measurements using your Apple Watch - Apple Support