Earlier quoted context omitted.
Isn’t battery a consumable and thus not covered by warranty by default? (Unless it has a manufacturing defect)
Is it reasonable to consider an element of a device a consumable if it is not user replaceable?
After going into the Apple store, they said that the battery was a "consumable part" and therefore not covered by the warranty. However, when I asked what the part number was and how I could order a replacement myself, they said that the batteries weren't serviceable and even they had to replace the keyboard unit as that contained the battery and it was all glued together.
I pointed out that they've therefore designed this product to fail after a few years as you can't order replacement batteries as a consumer, and they agreed to replace it for free.