To go for the official rating, up to the iPhone 14 it was 80% of the original charge after 500 cycles [0] and got improved (1000 !) later.

500 cycles can be a lot if you mostly keep it as a standby device to stay reachable, but not that much if you actually use the phone everyday.

That's less than 2 years if you completely drain the phone at least once a day. Our kid easily goes through two full charges in a day, especially on weekends. It really depends on what you use your phone for.

Also I think some people live with a < 70% battery without really minding it much. That's IMO only viable if you don't have a winter, where the battery efficiency becomes so worse. That's the combination of weak battery + poor weather that triggered the phone shutdown for me when BatteryGate was the rage.

[0] https://support.apple.com/en-us/101575

I use an iPhone SE2 that I got refurbished in the past 6 months by Apple. I couldn't replace just the battery, because the rear glass had a crack in it. This thing is a mess, refurbishing it feels like a waste of money. It runs out of battery almost daily, has terrible multi-second camera lag when I open the camera app from the lockscreen. Often the phone will just have like a quarter second of UI lag for no obvious reason. The experience is overall very slow and frustrating, an enormous degradation from when I got it as a gift 4 years ago (part of why I'm still using it).

It's a shame, because I like the phone a lot otherwise.