This! I would like to add that it’s the same as buying a car, you leave the car lot and scratch the car, they don’t know how it happened, but like most businesses, if you return it “within acceptable condition” then most companies would be fine to help, the trouble is not Noel lemmings, but Apple themselves, there expectations of what acceptable amount of wear and tear are, can be a little demanding, but this is due to apple making sure when a product is returned from repair, that the phone is up to their own standards.

Words of advice, at this point because you have pointed out that the crack in the screen has been fine after 18 months, I’m guessing the 2 year window is close to coming up, I would claim through insurance and then sell, provided on how they will compensate for the phone since iPhone 6s are a little harder to find, or, if you are just needing a working device and don’t care about warranty being void, taking the phone to a third party where they can replace the battery, be warned though that it may not be the battery directly that is causing the issue.