On the Mac, when you’re done
with an app you quit it. Many people think the same is true on the
iPhone, where you can double-press the Home button to access the App
Switcher and then swipe up on an app to quit it. But just because you
can do it doesn’t mean you should. Worse, contrary to what some people
believe, quitting iPhone apps will likely hurt battery life.
iOS thinks differently about how apps
run. When you’re using an app—say, Safari—it’s accessing the iPhone’s
CPU and radios and thus using battery power. However, a few seconds
after you press the Home button to return to the Home screen or lock the
screen by pressing the Sleep/Wake button, iOS puts the app into a state
of suspended animation. In that state, it’s not using CPU or battery
power, but it does remain resident in memory, which turns out to be
important.
Imagine that you next open Notes,
which becomes the active app and starts consuming CPU, memory, and
battery resources. Tap a Web link in a note, and iOS activates Safari
and suspends Notes. Because Safari was suspended and thus is still in
memory, it’s faster and easier for iOS to activate it than to launch it
from scratch.
As you continue switching among apps,
there won’t be enough memory for each app to remain suspended, so iOS
quits apps to free up enough memory. There’s no way to know when iOS has
done this; it’s invisible to the user. If you try to help iOS by
quitting apps manually, you’ll force it to waste more resources later
when those apps have to be launched afresh. You can get a sense of this
by swiping far to the right in the App Switcher; it probably lists many
more apps than you’d expect. That’s not a list of running apps; it’s a list of previously used apps.
So, 98% of the time, there’s nothing
to gain and some speed and battery life to lose by quitting apps. But
there are two legitimate reasons to quit apps: to restart a frozen or
confused app, or to prevent certain background apps from using power
unnecessarily.
Although it’s unusual for iOS apps to
freeze or misbehave, it can happen, so if an app isn’t responding, or
if it’s acting weirdly, quit it. That usually solves the problem; if it
doesn’t, restart, or you might need to download an update or delete the app and
reinstall it from the App Store.
iOS allows some apps to run in the
background instead of being suspended. For instance, if you use Maps,
you want it to keep tracking your location and providing turn-by-turn
navigation even if you’re using Podcasts. Similarly, iOS allows some
apps, like Skype, to listen for incoming calls in the background. There
are a few other categories of allowed background apps—audio apps like
Podcasts, for instance—but in all cases, if you’re trying to preserve as
much battery life as possible, consider quitting background apps whose
services you don’t need. For example, if you park before arriving at
your destination, you might quit Maps to ensure that it doesn’t continue
to track your location. And if missing an incoming call is less
important than saving some battery power, quit Skype.
But these are infrequent exceptions
to the rule. Most of the time, quitting apps is a waste of both your
time and your iPhone’s battery.
