Apps can be “closed” in iOS by double-clicking the home button to bring up the multitasking switcher and swiping an open app up to dismiss it. Whether this actually does anything to battery life has always been a point of speculation.
Some users claim leaving apps open and ready to switch back to leads to increased battery life because the app is still running, or least appears to be. Others point to Apple’s own support pages on running apps which state “there’s no need to force an app to close unless it’s unresponsive,” implying closing an app will do nothing to improve battery life.
There is no obviously easy answer though. Initially, assuming that an “open” app is consuming battery may be logical, until you realize the app isn’t really open at all when you’re just staring at its thumbnail in the multitasking carousel. It resumes immediately when opened, but is it still using the processor behind the scenes?
One particularly intrigued iPhone user decided to send an email to Apple CEO Tim Cook about the issue. The 9to5Mac reader asked Cook whether he quits all his apps when he’s finished using them and whether he considers it necessary, writing “Hey Tim, Do you quit your iOS multitasking apps frequently and is this necessary for multitasking?”
Although Cook never replied, a high-ranking executive on the iOS team did. Craig Federighi, iOS chief, intervened, saying he would offer his input instead of asking Tim. The headers of the emails have been verified, confirming the conversation is legitimate.
Federighi’s response is succinct and matter of fact. His answer: “No and No.” In the eyes of the person responsible for an iPhone’s software, “closing” apps from the multitasking switcher has no effect on battery life and is an unnecessary practice.
iOS apps are only actually “in the background” if they register a background activity with the system. These activities can be viewed and controlled from the Settings app to limit when an app can run in the background.
An app that has been opened by the user and then left in the multitasking UI is suspended as soon as the user brings a different app to the foreground though. Its state is frozen and saved to memory for an instant response when the user switches back to it. This consumes no more power than if the user dismisses it from the multitasking switcher by sliding it out of view.
This isn’t the first time high-ranking Apple execs have responded directly to customer enquiries made via the company’s public contact form. In the past, Tim Cook has replied to a user asking for Siri to come to Italy, continuing a trend started by Steve Jobs.
