Does closing all my apps save battery?

Liz's phone is at 12%. She has a long afternoon ahead. So she does what so many of us do in a battery emergency: she opens the app switcher and starts swiping. Away goes the map. Away go the messages, the camera, the shopping app, the weather.

Dan winces. “That usually won't help.”

Those apps were asleep

When you leave an app, it doesn't keep running in the background like a TV left on in an empty room. Your phone pauses it, almost right away. The app sits there, frozen in place, using next to no power, ready to pick up where you left off.

The row of apps in the switcher looks like a list of things your phone is busy doing. It mostly isn't. It's closer to a list of bookmarks: “here's where you were”.

Apple and Google both say as much. Apple's support page says you should close an app only if it's unresponsive. Google's documentation for app makers explains that Android keeps the apps you've left paused in memory, and clears them out by itself when it needs the space. There's nothing for you to manage.

Apple's head of software, Craig Federighi, was once asked whether he quits his apps, and whether it's necessary for battery life. His answer: “No and no.”

Closing them can cost a little

Here's the twist. When you close an app, the next time you open it, it has to start from scratch: load itself again and rebuild where you were. That takes more work, and more power, than simply waking up a paused app.

“So I've been making it worse?” says Liz.

A tiny bit, says Dan. The difference is small. But it's the opposite of what the swiping was meant to do.

So what is eating the battery?

Mostly, the screen. A big, bright screen is one of the hungriest parts of any phone, which is why both Apple and Google put brightness at the top of their battery tips.

Then there are the apps that really are working. A few kinds of apps are allowed to keep going after you leave them, because you want them to: navigation giving you directions, music playing in your earbuds, a call, a big download. Those really do use power, and they're the reason closing an app isn't always pointless.

You don't have to guess which ones they are. Your phone keeps score. On an iPhone, open Settings → Battery. On a Pixel, it's Settings → Battery → Battery usage, then View by apps. Other Android phones have something similar under Battery.

Liz looked. Top of the list, by a mile: her cat video app. Not running in the background. She'd just been watching a lot of cat videos.

What the video left out

Low Power Mode. If your iPhone is running low, Low Power Mode is the real emergency button. Apple says it dims the display, turns off Background App Refresh (apps fetching new content while you're not looking), and pauses things like photo syncing and automatic downloads. Turn it on in Settings → Battery, or from Control Center. Pixel phones, and many other Android phones, have a Battery Saver under Settings → Battery.

Frozen is different. If an app is stuck, won't respond, or is acting strangely, closing it is exactly the right move. That's the one case Apple's advice is for.

So swiping apps away rarely saves battery. Bright screens and busy apps are the real drain.

What you can do

• Turn down the brightness, or turn on auto-brightness (on Pixel: Settings → Display & touch → Adaptive brightness).
• Check which apps really use your battery: Settings → Battery. Menu names vary a little by phone.
• Low on battery? Turn on Low Power Mode (iPhone) or Battery Saver (Android).
• Leave your apps alone, and close one only if it's frozen.