Not surprising with all its features, but for wearables, that's a killer. My Fitbit can do 5-6 days, and I would consider that on the shorter end of decent battery life.
I haven't delved into wearables yet. I mostly have used my iPhone 5s (now 6) for the motion tracking, but it certainly doesn't catch everything (let alone doesn't catch vitals) since I don't carry it everywhere.
My biggest complaint with the Fitbit is the lack of any battery meter on the device itself. Unless you sync frequently, you wouldn't know when your battery is running low.
However, this is better than many of the smart watches to me, why have a large circular face?
Plus the price point of $199 isn't bad at all.