At this point, I have no other advice to offer. I have not done the iOS 11 updates, because so many people I know saying they are having the same issue, as well as complaints I've read online about this too.
What have you done to try and correct it or slow the battery drain, beyond doing the 2 newest iOS updates?
If the battery draining is still happening after the latest updates, you should contact Apple directly; it shouldn't cost you anything, since it appears to be a wide-spread problem. Also, please contact them about it here: https://www.apple.com/feedback/