In this mode the smartscreenmcomes on  whenever you lift and look at your wrist. The LCD screen is always on but glancing at it will power on the smartscreen. If you leave in the morning at 8am on a full charge you will get up to about 8pm the following evening. So it is either a good day's full use or just a bit light to make two full days.  What works for me here is to just charge it when I wake up and before I leave, which gets me through a full day and the next night.