http://www.overthought.org/blog/2014/the-ultimate-guide-to-solving-ios-battery-drain
What most people tell you is that closing your apps will save your battery life because it keeps the apps from running in the background.
Wrong.
Yes, it does shut down the app, but what you don't know is that you are actually making your battery life worse if you do this on a regular basis. Let me tell you why.
By closing the app, you take the app out of the phone's RAM . While you think this may be what you want to do, it's not. When you open that same app again the next time you need it, your device has to load it back into memory all over again. All of that loading and unloading puts more stress on your device than just leaving it alone. Plus, iOS closes apps automatically as it needs more memory, so you're doing something your device is already doing for you. You are meant to be the user of your device, not the janitor.
God artikkel om batterisparing, skrive av ein som tidlegare jobba i Genius Bar i ein Apple-butikk.