We're not sure exactly how long the battery would last in watch mode because we couldn't go that long without using all those functions. (digitaltrends.com)
But for the time being it is wait and watch mode on this one. (bachatkhata.com)
Switch to a traditional watch mode, using the monochromatic screen, and it'll last 30 days before you have to plug it back in using the magnetic charger. (9to5google.com)