There are times that an app in your iPhone is eating a lot of battery juice. Even if you’re not using them, they are still in the background and eats up power juice. Or sometimes you may have forgotten to close an app, draining your iPhone battery
So, how do you manage to see how much battery your various apps use? You can open up Settings that will report which apps have used how much battery, and for how long, over the past day or week. It’s a very handy screen indeed.
The iPhone battery setting is great. It’s a really useful feature for tracking down rogue apps. It’s the first way to know when the battery runs down faster than usual. You can then uninstall the apps you don’t bother using, or disable their background process so they will not be a pain in the head. You can do this by simply selecting them through the background App refresh.
Source: IT Black Spot