I will never use a smartwatch that won't last 4-5 days without charging.
It is the sole reason I gave in and got a Pebble; and now that my watch's hardware broke and the company was absorbed, I don't plan on buying another smartwatch unless I get an offer as good as that.
To achieve what they did, Pebble went with a low resolution screen and a low-power microcontroller with their own OS. If Swatch wants to do the same, they have my attention.