Does swiping away every app save your battery?

Most of the apps lined up in the recent apps screen are not running. They are paused. Once an app leaves the screen, your phone soon stops its work and keeps only its contents in memory so you can pick up where you left off. So the list is closer to a record of apps you opened recently than a list of apps that are working right now.

When memory runs short, the phone clears out the oldest apps on its own. It was designed from the start so that people would not have to tidy up for it.

An app still in memory opens instantly when you return to it, but an app you closed completely has to load from the beginning. Reading it from storage, redrawing the screen and reconnecting to the internet all happen at once, keeping the processor busy. A brief blank screen or loading indicator is what loading from scratch looks like.

If you close and reopen a messenger or map app you use many times a day, you end up spending a bit more of the battery you were trying to save.

In its support documentation, Apple advises closing an app only when it stops responding. Android is also designed so that the system clears out apps you are not using on its own.

Pressing a "memory cleaner" button makes the used-memory number drop sharply, which feels refreshing. But empty memory does not save battery, and apps soon fill it up again. Memory does not use less power just because it is empty, so keeping it filled and pulling apps out quickly is actually more efficient.

There are exceptions. If an app has frozen or become unusually slow, or a navigation app you have finished with keeps using your location, it is better to close it. Apps that keep working off screen, such as music or turn-by-turn directions, really do use power.

If you want to know which apps use the most battery, open the battery menu in Settings. It shows usage by app, so you can pick out only the ones that use noticeably more and turn off their background activity.