Android Wear watches typically have the screen always on, and in the case of the OLED one (LG Urbane) I've got that means bright enough to see my way through a dark room. I usually wear mine overnight (with the screen off) for sleep tracking, and after 23h it's usually around 50%. I'd be quite happy suggesting you'd get two full days' use out of it, especially if you don't keep it awake all night.