That is genuinely shocking to hear. You have to be like 3+ sd above the mean. Do you know how many charge cycles you have? I recall that most batteries need replacing after 300-500 cycles.
Edit: I just googled it. Apple claims that the iphone 17 should handle 1000 full charge cycles before reaching 80% capacity
I also believe apple’s claim is assuming optimal conditions. Real life is going to do a fair bit worse. So likely 700-1000 cycles for 80% if the pattern holds up.
If you are using “needs replacing” to mean “the device will be non-functional or risk permanent damage”, you can go significantly lower than 80%. In fact, I think most devices could go down to 0% battery health unless the battery swells.