It's so weird to me why they limit this to the 15 series. Older phones clearly have this information (you can get this data with coconutBattery) and having this information is hardly a killer feature that makes people upgrade.
"Better cameras? Meh. Faster chip? Meh. Titanium? Meh. Battery cycle count in device settings? AH HELL YEAH SIGN ME UP."
Totally agree. Some of the software gatekeeping from Apple frustrates the hell out of me because when you’re spending so much on a self professed premium device something as small as battery age shouldn’t be device specific.