Forerunner 255

The new 255 comes in two sizes, a standard 46mm and a smaller 41mm for those with a smaller frame. 

The standard 46mm has a 22mm band while the smaller 41mm has a 18mm band width. 

Weight: 39g/49g

Water rating: 5ATM (waterproof and comes with a swim activity to measure laps and strokes)

Battery Life: Up to 12 days (41mm)/ up to 14 days (46mm)

Battery life (GPS only) up to 20 hours(41mm)/ up to 25 hours (46mm)

Battery life for GPS + Music: up to 5.5 hours(41mm)/ up to 6.5 hours (46mm) only available in the Music version here. 

Battery life Dual band + all systems, no Music: up to 13 hours(41mm)/ up to 16 hours (46mm)