How to Enter & Exit Apple Watch Power Reserve Mode
Though Apple Watch battery lasts a reasonably long amount of time, having a powered off or dead battery Apple Watch on the wrist is not particularly useful. One helpful tip when you approach the lower bounds of battery remaining is to switch into Power Reserve Mode on Apple Watch. Power Reserve Mode turns the Apple Watch screen into just a watch, allowing you to at least tell the time when the battery gets quite low.
With Power Reserve Mode enabled, Apple Watch will cease all functions except a limited onscreen clock display. While you can enter Power Reserve at any time, this is not something you’d probably use for fun since it disables basically all features of Apple Watch like fitness tracking and heart rate monitoring, messaging, notifications, etc. With that said, it’s an incredibly effective way to continue to use the Apple Watch as a time-telling device in situations when it would otherwise run out of battery.