Prevent Apple Watch from running out of battery with this handy tip…
If you don’t have your wireless charger to hand, then enabling Power Reserve mode can extend the life of your Apple Watch by another 2-3 days. To enable it, press and hold the side button then slide the Power Reserve slider to the right. All functions except the watch face are now disabled.
To see an estimate of how long Apple Watch will work in Power Reserve mode, open the Apple Watch app on iPhone and go to General > Usage, then swipe down to the bottom of the screen.