You double-click the Home button and swipe your apps off the top of the screen: Good idea or bad idea? There’s been some confusion lately about whether closing out your iPhone and iPad apps is helpful or harmful, especially with regard to battery life. I’ve always said it’s a good idea: Close Out Your Apps is tip #4 of my article about how to save iPhone battery life.
In this article, I’ll explain why closing out your apps can be helpful for your iPhone battery life, provide excerpts from Apple Developer documentation to support that, and include some examples from real-world tests I did using Apple Developer Tools and my iPhone.
When I write, I want the information I provide to be helpful and easy for everyone to understand. I usually don’t get too technical, because my experience working at an Apple Store has shown me that people’s eyes begin to glaze over when I start talking about processes, CPU time, and the app life cycle.
In this article, we’ll dive a little deeper into how apps work so you can make an informed decision about whether closing out your iPhone or iPad apps is right for you. First, we’ll talk about the App Life Cycle, which describes what happens from the moment you open an app until it closes and is cleared from memory.
The App Life Cycle
There are five app states that make up the app life cycle. Every app on your iPhone is in one of these states right now, and most are in the not running state. Apple Developer documentation explains each one:
- When you press the Home button to leave an app, it goes into the Background or Suspended state.
- When you double-click the Home button and swipe an app off the top of the screen, the app closes and goes into the Not Running state.
- App states are also referred to as modes.
- Apps in Background mode are still running and drain your battery, but apps in Suspended mode do not.
Swiping Up Apps: Closing or Force-Quitting?
To clear up some confusion about terminology, when you double-click the Home button on your iPhone and swipe an app off the top of the screen, you are closing the app. Force-quitting an app is a different process that I plan to write about in a future article.
Apple’s support article about iOS Multitasking confirms this:
“To close an app, double-click the Home button to see recently used apps. Then swipe up on the app you want to close.”
Why Do We Close Out Our Apps?
In my article about how to save iPhone battery life, I’ve always said this:
“Once every day or two, it’s a good idea to close out your apps. In a perfect world, you would never have to do this and most Apple employees will never say you should… A lot of battery drain issues occur when an app is supposed to close, but doesn’t. Instead, the app crashes in the background and your iPhone battery beings to drain without you even knowing it.”
In short, the main reason I recommend closing out your apps is to prevent your battery from draining when an app doesn’t enter the background state or suspended state the way it should. In my article about why iPhones get hot, I liken your iPhone’s CPU (central processing unit; the brains of the operation) to a car engine:
If you put the pedal to the metal for an extended period of time, the car engine overheats and it uses a lot of gas. If an iPhone’s CPU is revved up to 100% for an extended period of time, the iPhone overheats and your battery drains quickly.
All apps use the CPU on your iPhone. Normally, an app uses a large amount of CPU power for a second or two when it opens, and then throttles back to a lower power mode as you use the app. When an app crashes, the iPhone’s CPU often gets stuck at 100%. When you close out your apps, you make sure this doesn’t happen because the app returns to the not running state.
Is It Harmful To Close An App?
Absolutely not. Unlike many programs on your Mac or PC, iPhone apps don’t wait for you to click “Save” before they save your data. Apple’s developer documentation emphasizes the importance of apps being ready to terminate at the drop of a hat:
“Apps must be prepared for termination to happen at any time and should not wait to save user data or perform other critical tasks. System-initiated termination is a normal part of an app’s life cycle.”
When you close an app, it’s OK too:
“In addition to the system terminating your app, the user can terminate your app explicitly using the multitasking UI. User-initiated termination has the same effect as terminating a suspended app.“
The Argument Against Closing Out iPhone and iPad Apps
There is an argument against closing out your apps, and it’s based in fact. However, it is based on a very narrow view of the facts. Here’s the long and short of it:
- It takes more power to open an app from the not running state than it does to resume it from the background or suspended state. This is absolutely true.
- Apple puts a lot of effort into making sure the iPhone operating system manages memory efficiently, which minimizes the amount of battery apps use when they remain in the background or suspended state. This is also true.
- You are wasting battery life if you close out your apps because it takes more power to open iPhone apps from scratch than the operating system uses to resume them from the background and suspended state. Sometimes true.
Let’s Look At The Numbers
Developers often use CPU time to measure how much effort an iPhone has expend to accomplish tasks, because it can have a direct impact on battery life. I used an Apple developer tool called Instruments to measure the impact of several apps on my iPhone’s CPU.
Let’s use the Facebook app as an example:
- Opening the Facebook app from the not running state uses about 3.3 seconds of CPU time.
- Closing any app wipes it from memory returns it to the not running state and uses virtually no CPU time – let’s say .1 seconds.
- Pressing the Home button sends the Facebook app to the background state and uses about .6 seconds of CPU time.
- Resuming the Facebook app from the background state uses about .3 seconds of CPU time.
Therefore, if you open the Facebook app from the not running state (3.3), close it (.1), and open it again from the not running state (3.3), it uses 6.7 seconds of CPU time. If you open the Facebook app from the not running state, press the home button to send it to the background state (.6), and resume it from the background state (.3), it only uses 4.1 seconds of CPU time.
Wow! In this case, closing out the Facebook app and reopening it again uses 2.6 more seconds of CPU time. By leaving the Facebook app open, you’ve used around 39% less power!
And The Winner Is…
Not so fast! We need to look at the big picture to get a more accurate appraisal of the situation.
Putting Power Usage In Perspective
39% sounds like a lot, and it is – until you realize how infinitesimally small the amount of power we’re talking about is in comparison with the power it takes to use your iPhone. The argument against closing out your apps sounds great until you realize it’s founded on a statistic that doesn’t matter.
As we’ve discussed, you’ll save 2.6 seconds of CPU time if you leave the Facebook app open instead of closing it. But how much power does the Facebook app consume when you use it?
I scrolled through my newsfeed for 10 seconds and used 10 seconds of CPU time, or 1 second of CPU time per second I used the app. After 5 minutes of using the Facebook app, I would have used 300 seconds of CPU time.
In other words, I would have to open and close the Facebook app 115 times to make as much of an impact on battery life as 5 minutes of using the Facebook app. What this means is this:
Don’t decide whether or not to close out your apps based on an insignificant statistic. Base your decision on what’s best for your iPhone.
But that’s not the only reason why closing out your apps is a good idea. Moving on…
Slow And Steady CPU Burn In Background Mode
When an app enters background mode, it continues to use battery power even when your iPhone is asleep in your pocket. My testing of the Facebook app confirms this happens even when Background App Refresh is turned off.
After I closed the Facebook app, it continued using CPU even when the iPhone was off. Over the course of one minute, it had used .9 seconds of additional CPU time. After three minutes, leaving the Facebook app open would use more power than it would have if we closed it right away.
The moral of the story is this: If you’re using an app every few minutes, don’t close it every time you use it. If you’re using it less frequently, it’s a good idea to close the app.
To be fair, many apps go straight from background mode into suspended mode, and in suspended mode, apps don’t use any power at all. However, there’s no way to know which apps are in background mode, so a good rule of thumb is to close them all. Remember, the amount of power it takes to open an app from scratch pales in comparison to the amount of power it takes to use the app.
Software Problems Happen All The Time
iPhone apps crash more frequently than you may realize. Most software crashes are minor and don’t cause any discernible side-effects. You’ve probably noticed it before:
You’re using an app and all of a sudden, the screen blinks and you end up back on the Home screen. This is what happens when apps crash.
You can also view the crash logs in Settings -> Privacy -> Diagnostics & Usage -> Diagnostic and Usage Data.
Most software crashes are nothing to worry about, especially if you close out your apps. Often times, an app that has a software problem just needs to be launched from scratch.
An Example Of A Common Software Problem
It’s lunch time and you notice your iPhone battery has drained to 60%. Over breakfast, you checked your email, listened to music, sighed over bank account balance, watched a TED talk, flipped through Facebook, sent a Tweet, and checked the score from last night’s basketball game.
Fixing A Crashing App
You remember that a crashing app can cause your battery to drain quickly and that closing the app can fix it, but you don’t know which app is causing the problem. In this case (and this is real), the TED app is burning through CPU even though I’m not using my iPhone. You can fix the problem in one of two ways:
- Connect your computer to a Mac, download and install Xcode and Instruments, enable your iPhone for development, set up a custom test to inspect the individual processes running on your iPhone, sort them by CPU usage, and close the app that’s causing your CPU to stay revved up to 100%.
- Close out your apps.
I choose option 2 100% of the time, and I’m a geek. (I gathered the information for this article using option 1.) Reopening your apps from the not running state uses more power than opening them from the background or suspended state, but the difference is negligible compared to the significant power drain that happens when an app crashes.
Why I Believe Closing Out Your Apps Is A Good Idea
- Even if you close your apps every time you use them, you will not see a difference in battery life because the amount of power it takes to open an app is insignificant compared to the amount of power it takes to use the app.
- Apps that stay running in background mode continue using power when you’re not using your iPhone, and that adds up over the course of a day.
- Closing out your apps is a good way to prevent serious software problems that can cause your iPhone battery to drain very quickly.
Close Out This Article
This article is more in-depth than the articles I usually write, but I hope it was interesting and that you learned something new about how apps run on your iPhone. I close out my apps a few times a day, and that helps me keep my iPhone running as smoothly as possible. Based on the tests and my first-hand experience working with hundreds of iPhones as an Apple tech, I can confidently say that closing out your apps is indeed a good way to save iPhone battery life.
Thanks for reading, and remember to pay it forward,