My 15 pro Max has just dropped to 87% over 374 cycles, first use Oct 2023. I feel this battery is weakening at a faster rate than my previous iPhones. I have been travelling quite a bit for work over this past year and as such have perhaps used the phone more than I ordinarily would, and I have been charging it more often with my Dell 65w laptop charger when away from home. However, when at home I wirelessly charge at 7.5w (max rate supported by iPhones over Qi-1) using my 10w Qi-1 charger. I plan to pass this phone down in the family next year when the 17 Pro Max comes out as I do every two years when I upgrade. I will have to replace the battery for £95 at the Apple store before I do this time though.
My previous 13 Pro Max which is still in the family is now on 84% at just over 3yrs old, so my 15 Pro Max really is not doing well in comparison. I have wondered whether more frequent charging using the 65w charger has degraded the battery faster, it can certainly get quite warm when fast charging, especially if the phone is in use at the time, which I now ensure I avoid.