[ajonit]

Would love to see what others have to say on this but I suspect Apple replacement batteries are inferior compared to the one that comes with the new phone. 4 years of usage and battery max capacity was around 76%. I replaced my iPhone X battery last year. The new one I got is at 86% already and it is not even 12 months. (No usage pattern change. I replaced it from an Apple Store.)

[kelnos]

I wonder if that can be accounted for by the fact that the software of today is more taxing than it was four years ago. You're probably using more battery charge every day today than you were four years ago to do the same things. That increases wear on the battery and will reduce its lifetime.