iOS 11.0.3, iPhone 7S, language setting English
There certainly is an issue with phone battery discharging fast, after upgrading to iOS11. Even the two successive updates do not seem to solve the matter. I suspect that the reason is in the application CONTACTS. I checked my power usage and a remarkably high portion of my battery capacity was used by the app CONTACTS. It was 25%, even though the app was on screen only for 2 minutes. It seems to be running on background, trying to achieve something, that does not work now.
This probably may be connected to the other issue that also irritates me very much, and this is the failure of the app PHONE or the app CONTACTS to open the app MESSAGE properly. If you tap "send message" on a contact in CONTACTS or in RECENT, it just fails. Also the app MESSAGES uses too much power, in relation to its time on screen. It also seems to be attempting something on the background. Is there a corelation?
One other thing. Sometimes after receiving a call or dialling a contact, it fails to appear in the RECENT list.
This apps need to be restarted too, helps, not always.
To support my opinion of the app CONTACTS draining the battery, see the enclosed print screen of my battery usage screen.
In the good old days in the automotive industry, there was a golden rule: NEVER TOUCH A RUNNING SYSTEM. Wish this was true in IT too.
Have a nice day.
Eddie