The battery in the Apple Watch lasts approximately 18 hours, depending on use. If your battery gets too low, you can put the watch into Power Reserve mode so you can see the time for up to 72 hours.
All Apple Watch functionality shuts down except the ability to keep and display the time, which can only be displayed by pressing the side button on the watch. The time displays for six seconds. All apps, glances, and other general watch functionality are not available in Power Reserve mode and your Apple Watch and iPhone won’t communicate.
The result of putting your watch in Power Reserve mode is a sharp decrease in power usage. You’ll have basic watch functionality for a longer period of time until you have a chance to recharge your watch battery.
We’ll show you how to enable Power Reserve mode and how to get your watch back to normal mode. There are few ways you can enable Power Reserve mode.
If you’ve run down the battery on your watch to 10 percent, the “Low Power” screen displays, as shown in the image at the beginning of this article. Tap the “Power Reserve” button. The following confirmation screen displays. Tap “Proceed” to put the watch in “Power Reserve” mode.
You can also put the watch in “Power Reserve” mode using Glances. Swipe up on the main watch face and swipe right or left until you find the Battery glance. Tap the “Power Reserve” button.
The same confirmation message displays as seen from the “Low Power” screen, but in green instead of red. Tap “Proceed” to put the watch into “Power Reserve” mode.
Finally, you can turn on “Power Reserve” mode by pressing and holding the side button until you see the following screen.
NOTE: If you’ve applied a Passcode to your watch, the “Lock Device” button would also be available on this screen.
Drag the “Power Reserve” slider button to the right to turn on the “Power Reserve” mode. When turning on “Power Reserve” mode using this method, there is no confirmation screen.
Now the only functionality is keeping and viewing the time, which displays in green when you press the side button.
To disable “Power Reserve” mode and return your Apple Watch to normal mode, you need to reboot the watch. Press and hold the side button until you see the Apple logo. The watch will boot into normal mode. Note that this only works if you have enough battery life to boot the watch. You can attach the charger to the watch while it’s booting if you don’t have enough battery power.
“Power Reserve” mode makes your smartwatch into a very dumb watch. While your Apple Watch is in “Power Reserve” mode, there are things that “normal” watches (non-smart watches) can do that the Apple Watch can’t do. But, if you need to make your battery last longer, “Power Reserve” mode is helpful.