You can see which of your apps are using the most battery power. Go to Settings > General > Usage > Battery Usage. You can see which apps have used the most energy in the past 24 hours and the past week. Note that high ranking apps are not necessarily battery hogs. It may be you frequently used that app or the app was downloading or uploading data in the background. Apps you should be concerned about are those that appear at the top of the power consumption list even though you haven’t been using them much.