I phone 8 plus battery just all of a sudden started draining out of control!!
My iPhone 8 Plus had been running on iOS 11 since I got it. Mainly because of all the talk of 11.x and up killing the battery so fast. And my phone was having no issues on 11. Until 3 days ago I left for work fully charged and by noon I was at 10%. Super fast. Not knowing why or how. I already do all the iPhone life hacks for longer battery life. So my wife talked me into updating. So I did and it updated my phone to iOS 12 and still no better. With so many 8 plus phones w the same issues it seems to me that this is more than an iOS issue