I would double check a few things.
Make sure you have applications not refreshing in the background. To toggle these, go to Settings > General > Background App Refresh. I would toggle off any unnecessary ones.
I would also verify that your apps are closed by double clicking the home button and swiping up on any apps you are not using.
Lastly, to see what applications are using the most battery life, go to Settings > Battery. Allow the "Battery Percentage" to load and see what apps are using your battery.
If none of these resolve the issue, I would recommend getting a diagnostics test run on your iPhone by an Apple store or an AASP (Apple Authorized Service Provider).