Conversely, smartphones could have batteries 1/100th the size of their current batteries and still have the same battery life. Nothing says that if we want to use this tech in smartphones we have to have 100x the battery life (although that would be fantastic). Even 2x or 3x would be game-changing for power users, especially if battery performance degraded at only the same rate that current smartphone batteries do.

You wouldn't need a huge array of coin cell batteries; one coin cell might well be enough.