The new one isn't actually longer. It's just that they changed how they measure it. It assumes 16 awake hours and 8 asleep hours, so the watch lasts 24 hours,

The new one isn't actually longer. It's just that they changed how they measure it. It assumes 16 awake hours and 8 asleep hours, so the watch lasts 24 hours, but only when you are sleeping and thus not using it for 8 hours.