Chosen Solution
My battery had gotten old and since my warranty was already gone, I replaced it with a high quality replacement. It wasn’t a crappy one from China or something. And this worked for almost 6 months. Then I updated to iOS 11. After two days I was low on battery when my iPhone restarted twice then died. I plugged it in over night and tried to turn it on using every trick in the book. I took it to the Genius Bar and they did the same things I did to no avail. I had smartly saved my older crappy battery and when I turned home I opened up my phone and put in the old battery and, presto it worked perfectly. I know apple doesn’t support 3rd party screens and batteries but I’m pretty sure these two batteries are completely identical in all but casing. I’m writing this question because I want to know what went wrong and how replacing the battery fixed it.
Sounds purely coincidental. Probably either the replacement battery went faulty or charging circuit has an issue. You will notice charging circuit is at fault if phone does not turn on once the battery goes flat.
