Launch the Watch app from your Home screen. Tap on your Apple Watch at the top of the screen. Tap the information button (looks like an "i" with a circle around it) Tap Unpair Apple Watch. Tap Unpair [Your] Apple Watch to confirm. You can also un-pair right on the Apple Watch: Press the Digital Crown to switch to the app launcher. Tap on the Settings app. read more
Open up the Apple Watch app on your iPhone and go into Notifications and turn off anything that you don’t need. Go to Settings > Brightness & Text Size on your Apple watch and reduce the brightness. On your Apple Watch go into Settings > General > Wake Screen and toggle off Wake Screen on Wrist Raise. read more
If your Apple Watch battery still dies fast after following the tips above, you may want to disconnect and reconnect your Apple Watch to your iPhone. To unpair your Apple Watch and iPhone, open the Watch app on your iPhone and tap the name of your Apple Watch at the top of the My Watch menu. read more