When battery saver is on, your PC temporarily turns off some things that use a lot of power, like automatic email and calendar syncing, live tile updates, and apps you’re not actively using. Using battery saver is the easiest way to extend battery life.
Select the Start button, and then select Settings > System > Battery . If you want battery saver to turn on whenever the battery falls below a certain level, select Turn battery saver on automatically if my battery falls below: and set it where you’d like. To turn on battery saver now and leave it on until the next time you plug in your PC, turn on Battery saver status until next charge.