The reason is that most apps are suspended and cease to utilize system resources once the user switches away. If you go back to the app, it springs back from its frozen state. Actively shutting down the app, however, forces your system to repeatedly reload the app, which can cause more stress on your phone and contribute to battery usage. The only apps that actively run after you switch away are pretty obvious, like a GPS navigator, audio recorder or your Spotify app that plays background music.
So how do you actively preserve your iPhone’s battery life? Disabling Background App Refresh, which automatically updates content on suspended apps, is one way. Keep in mind that Background App Refresh is smart about when it updates content, like when your phone is plugged in or when it’s already in active use, so it’s still not a big battery user. Location services are one of the biggest energy drainers, so turning them off for underused apps is another good way to preserve your phone’s life. For a more comprehensive view on your phone’s battery sucking culprits, go to the “Battery Usage” section under Settings. This will break down the biggest battery users on your device.
Not all smartphones freeze apps once you click away. Samsung Galaxy users will see longer battery life if they actively shut down running apps, as well as Nokia Lumia as well as other Android phones.
But iPhone toters, it’s not the apps: the reason why your phone keeps dying so quickly remains a mystery.