People choose the path of least resistance.

If you can quickly swap out an old phone battery with one you can purchase in a store, it's as easy as doing groceries.

If on the other hand you need to hand off your phone to a third party for repairs, and require people to make a backup of important data, maybe factory reset just in case, get a replacement device for the time without it, tell people you'll be unavailable for a bit... It's a big enough hurdle for people to think "well, guess it's a good enough excuse to upgrade to a new model". I've heard the latter too many times in my surroundings purely due to battery life issues.