Some athletes need battery life that's measured in days, not hours. The Suunto 9 was built with them in mind. It has three battery modes that offer from 25 hours to five days of battery life, and intelligent software to help you switch in between them. It pulls off this trick with a proprietary FusedTrack algorithm that combines motion and GPS data to accurately track your movements while reducing GPS power. It also has over 80 sport modes, a built-in heart rate monitor, a barometer, and a rugged case waterproof to 100 meters.