Just went to Apple Store Genius Bar appt for battery replacement on a 6S plus with 687 charge cycles %88 capacity (coconut battery app on Mac). The employee ran Apple’s diagnostics over WiFi connection with the 6S. Their system quoted capacity %95 of original battery design. So he said they couldn’t replace it period ($29 or $79), and the battery was unavailable anyways. I told them that the Apple phone rep who made this appt for me didn’t mention any of the criteria re: below %80 battery capacity. The Genius Bar guy went back to talk to someone and returned saying they could replace the battery for me. I appreciated the gesture, but I ultimately agreed with the guy in not replacing the 6S battery now and saving the $29 replacement offer until end of this year.