This probably exists, but a check in the app store as not revealed it: there are loads of battery monitor apps, but it would be helpful to have a battery monitor app with a graphical output. So between charges, the app would get the battery % left every 15 minutes, for example, and then simply plot % v time. We would then be able to get an idea as to what is increasing the battery drain by turning things off, e,g. Siri at present, and see visually whether that has made any difference.
I have seen no change in my iPhone SE battery runtime since upgrading to iOS 11, but the iPhone SE isn't capable of most of the new features that even iOS 10 introduced. With iOS 11 on my iPhone SE, Siri capability is much enhanced and there are more choices in the Control Center but otherwise not much has changed. I was easily getting two days per charge before the upgrade and I still am. Siri is on with all options enabled. Location Services is on but only while the apps are in use in all except one case. I am very conservative with Background App Refresh - that is a real battery hog. I allow only those apps that I really need it to use that. Very few, maybe 2 or 3 out of about 100 total apps. Screen brightness is set to auto and the backlit LCD screen uses little power anyway especially compared to OLED. An OLED screen can be expected to use a lot more power. The iPhone SE is a very basic, small screen phone, similar to the 5s and shares the same housing. The one thing I have an issue with on iOS 11 is that the Xmarks app that I so often used will not work with iOS 11. That is the Xmarks developers fault and they are being inundated with complaints.