It similarly showed 80+% battery health, but I showed them the battery charge history in Settings (dropped from 40% to 0% instantly) and they replaced it under warranty.
Happened a year and a half later, exact same scenario, and paid the ~$30 to get it replaced.
I suspect they didn't have any monitoring to detect or log the shutdowns at the time. But I find it extremely confusing why different Apple stores would have such different policies or manager discretion.
I may be mistaken, but I don’t believe there was any battery charge history (at least not accessible to users) in iOS at the time?
In any event, I am not sure the unexpected shutdowns would have manifested themselves as sudden reductions in charge. Once restarted, the iPhone reported a similar charge to before the shutdown.
I'd guess the date is a key factor, as I'm sure thousands of people showed up at the Apple store because they heard on CNN that their battery was broken.
At the time they just refused to even consider the possibility it was a genuine hardware issue. I got the lecture about batteries being consumable items, mine was somewhat degraded (82% health), etc. They suggested I do a software reset, etc.
I like to think maybe in hindsight someone at Apple HQ looked at the diagnostics from my Genius Bar visit as part of the decision to introduce throttling, and realised they were wrong.
I can vouch for this. My iPhone 6 was under 2 years old and had 82% battery health according to the Apple diagnostics when I experienced the unexpected shutdowns.
The shutdowns were frequent (at least once per day) and, because the phone had to be plugged in before it could be restarted, were incredibly frustrating.
I took it to an Apple Store. The Genius refused to acknowledge any fault. They ran the diagnostics which showed 82% and refused to replace the battery, even if I paid, as it was above their 80% threshold for replacement.
I spoke to the manager, and they stood firm. No replacement, even if I paid. I was extremely persistent and they simply would not budge.
The throttling resolved my shutdown problem.