我的iWatch 6， 九小时骑完车，仍然25%电池

Airplane mode; turn off wifi and bluetooth. 

Turn off "raise" to wake up display.

Do not listen to music with it

Only GPS and heart rate.

It's accurate only on forearm or upper arm. Not so accurate on the wrist (too much movement and too little flesh) if you care about accuracy. Actually, any wrist watch has this problem if you wear it only on the bony wrist.

iWatch是我的backup。 我用Garmin Edge Bike Computer to track GPS + Power + Heart rate.