FYI IOS 11.4
I updated to 11.4 a week ago and since then I have experienced terrible battery life, often needing to recharge every 3 hours of light use. I have a new replaced battery from APPLE's battery deal for iphone 6's.
What I found searching is you have to disable 5ghz wifi and use the 2.5. Since then my battery life is back to normal. Hope this helps someone.
Apple has already announced that they will provide batteries to those who are experiencing trouble after updating their device at $25.