Mine is at 90% health. Bought in November. In May it was 94% when I first complained. They tested it and declared it normal. It dropped another 4% after two more months. Again, Apple says it's normal, though when I persisted, the "genius" said it doesn't seem normal to him as I only have 95 charging cycles, and use it lightly. Their diagnostics say there's no issue, though they agreed to send it to their "depot" for further testing - apparently they'll have my phone for a week or so. They said it might result in the battery being replaced, or it could confirm a "normal" diagnosis and I'd be out of luck.
I say it's definitely not normal, a I'm really a light user. With almost the same use and charging pattern daily, sometimes the charge drops to 34% or so by the time I go to bed and charge it. Other times with similar usage, it is at 78% or so at bed time.
I have a fear that they will determine it's normal, and that it will hit 79% just after my warranty is up. So far, I'm not impressed with this $1400CAD purchase. I might have been impressed if Apple had just acknowledged maybe having some some bad units, and simply replaced it (or its battery) without hassle. I had to really press them to look further into it.
They did give me a loaner iPhone 8, but I was forced to wipe out my eSIM, and go back to a Nano Sim, as the iPhone 8 is their newest loaner. Seems a bit silly that they can't do loaners that handle eSIM. The tech made it sound like it was my fault for using eSIM. That rubbed me the wrong way! And I just know there will be a charge from my telco to redo the eSIM.
I'm starting to wonder about Apple. About 5 years ago when I had a battery issue (with a much lesser phone), they couriered me a new phone in 24 hours, with pre-paid shipping to return the bad unit. I did not get the same concern this time on what I consider a premium model.