PSA: Force Quitting Apps Hurts Battery Life §

I’m a phone voyeur. Whether on the train or in line at the market, I peek at what people are doing on their phones. I don’t read their messages and whatnot, but I like to see the apps people use in the wild. I’m like a cultural anthropologist, it’s a harmless designer pastime.

There’s one thing that I see all the time: people double-tapping their home button, then swiping up, up, up, up over and over until every last app card has disappeared. Then they return to the home screen and open an app that they just quit.

It’s extremely common on iPhone, but I see it on Android too. I’ve heard the reasoning: they’re not using the apps anymore, so they’re quitting them to save battery.

Just stop it. You’re not actually helping anything, in fact your making things worse.

Let me explain.

Multi-tasking on a mobile device is not like multi-tasking on a desktop or a laptop computer. There you can have dozens of apps open at a time, all of them are running and actively using memory. Force quit (or ctrl+alt+delete for Windows folks) exists because one of those apps can suddenly go astray; it can start eating up memory or CPU and literally grind the system to a halt. There has to be a way to get control back from that app, and so the feature exists to give you the ability to do just that.

On a mobile device, however, things are much more limited — I’ll go on here using iOS as a reference because that’s what I know best, Android is very similar.

Background Activity

On iOS, the operating system only allows specific kinds of tasks to happen when an app is closed. The scope is limited to exactly what you’d expect: playing music, tracking location (if you’re a map app for example), finishing up a network activity (like downloading a file), or to provide calling services if you’re an app like Skype. That’s it.

Network activity is time bound, so if an app wants to finish downloading a file it can tell iOS "Hey, I need 7 more minutes to finish getting this file before you kill me," and the OS will allow it. But after that, time’s up. In fact, iOS even limits the amount of time an app can ask for, all in the name of battery saving.

The other activities are allowed to go on until the user quits the app, or disengages the activity, for obvious reasons. You wouldn’t want Google Maps to stop giving you directions after 10 minutes when you’re driving somewhere you’ve never been, for example. Or, for that matter, Spotify to just stop playing music.

Quick aside: as of iOS 8, I believe, apps are allowed to wake up with a silent notification, and perform some activity in the background. This is generally used for news apps or a podcast app. When a new episode, or article, becomes available, the app can receive a notification to wake up and download it. This activity is considered normal network background activity and is also time-bound. The number of notifications to wake-up is also restricted over a given time period (5 times per day, for example).

App Switcher

So when people talk about "multi-tasking" on a mobile device, those are the few things they are referring to. When one double-taps the home button, what is being seen is not a representation of all of the apps that are currently running, but screen shots of the most recently used apps, suspended in time.

That’s right, these apps aren’t running (unless they’re doing one of the four things above). It is literally just a screen shot captured by the operating system the instant you tap the home button, or switched to a different app.

This is not a "multi-tasking" menu, it’s just a dumb app switcher. A way to quickly navigate back and forth between apps that you’re probably using right now. Just like pressing the Command + Tab keys on a Mac (or Alt + Tab on Windows).

So how does this actually affect battery life?

Here’s the bottom line: 99% (most likely 100%) of those apps aren’t running. They are paused; sleeping. The most recent ones are probably still in memory, so that when you switch back it resumes instantly. When you force quit an app in the switcher, the OS completely kills it, along with everything that it had already loaded into memory, and any state it was saving for you.

That means that the next time you tap on the app it’s literally being reborn. And guess what? That uses more processing time from the CPU, more memory as the OS starts to fill it back up with the things the app needs to run (and actually requires even more CPU time if it has to start transferring other apps out of memory to make room for this one again), and, if the app requires the network to pull information (like a Twitter client), then the radios are being powered back up to check for new updates. These things kill battery life.

That’s the opposite of what you’re trying to accomplish.

TLDR

Occasionally there are some reasons to force an app to quit form the app switcher, like if one of those 4 permitted background tasks has gone rogue, but this is super duper rare. Most of the time one does this out of the mistaken notion that battery life is being extended. It isn’t.

Mobile operating systems are designed from the ground up to be very good at managing the battery, it is literally its most important job.

Those apps in the switcher aren’t running the vast majority of the time, but the OS is keeping them there ready for you, suspended in time. Closing them doubles the work of the OS, probably powers the cellular and/or wifi radios back up, and wastes power.

So stop doing it. Tell your friends, tell your family.

Miscellaneous Other Things

  1. It’s rare, but the fact that articles like this have to be written to dispel mythical home remedies like these expose a design flaw in both iOS and iPhone hardware. The app switcher on a Mac or Windows is just the app icon, it’s super clear the action being taken. By showing a screenshot, Apple is insinuating things, mainly that the app is still working. As for why people continue to do the force quit for battery life maneuver exposes the hardware flaw: the damn battery doesn’t last long enough!

  2. I glossed over the point that sometimes force quitting an app is a legitimate necessity, mainly because the focus here is that most people do this under the mistaken notion that they’re saving battery life, but it’s also true that sometimes apps in the background can and do go rogue. Usually on accident, sometimes by design (as Facebook may have done in the past by playing silent audio while it was in the background to keep it awake under false pretenses). If you’re actually concerned that an app is being wasteful, Apple provides battery usage information and allows you to shut off background access on a per app basis in Settings.
     

  3. With iOS 9 on the iPad, Apple now allows apps to run side-by-side. This is actual multi-tasking. Those two apps are running at the same. When you tap the home button, or replace one of those apps with another, though, the app is suspended and the rules above apply.

  4. In addition to the wake-up on notification type I mentioned in the aside above, apps can make the same request locally to do something. If it isn’t a crucial operation that needs to be performed at a specific time (like a timer, or alarm clock, for example) the OS automatically bundles the requests together with the requests from other apps, and the OS itself, so that it can opportunistically perform the activities at the same time. In this way, the phone needs to power up the radios only once and performs many background activities, as opposed to powering up randomly, sporadically.

  5. If you want to learn more about how strict iOS is with background app activity, check out the official developer documentation.

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