Could the decision to support the 80% charging limit for only iPhone 15 be related to changes in battery chemistry? Does the iPhone 15 use a different battery chemistry? I ask because I have noticed my iPhone 15 charges to 80% way faster than my other phones and devices
Unlikely. Virtually all lithium batteries display similar characteristics with respect to charging.
Charging faster is something that can be variable between chemistries, but typically batteries are fine with charging quite quickly in the first 80% regardless, and can be made to tolerate fast charging (though usually you sacrifice a little bit of lifespan or total capacity to increase that tolerance)
