Swipe up on the watch face, then swipe to the Power glance
Tap Power Reserve, then tap Proceed.
You can also press and hold the side button until you see the power reserve slider appear, then drag it to the right.
Once in Power Reserve mode the Apple Watch continues to keep and display time, but other apps aren’t available for use.
To return to normal power mode, press and hold the side button to restart the Apple Watch. There must be sufficient charge in the battery for this to work.
Please note: The Apple Watch automatically enters Power Reserve mode if the percentage of battery charge remaining drops below approximately 10 percent.
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