Were you on iOS 18? I went to 18.1 beta and the battery is better on my 15PM.15 Pro Max 256 GB blue titanium to 16 Pro Max 256 Gb Black Titanium
I upgraded basically because of the screen size and the battery.
The battery on the 15 Pro Max was horrible, last week it was already at 91% health.
I notice it more fluid, the quality of the screen is very noticeable, and the 6.9 inches, and the battery is much better, the 15 Pro Max for me in terms of battery is not very good, I lasted longer the 13 Pro Max ...