Batteries are not expensive. If the battery was easily replaceable and the phone could detect a defective battery (perhaps a sensor to detect the start of swelling?) then eeking the most life possible out of the battery would be something few people would care about. They'd just replace the battery. Extending the usable life of a battery seems like a reaction to the reprehensible practice of not making batteries easily replaceable. Yet another business practice (like elaborate packaging) that wastes energy, time, and resources.