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All-day battery life is based on 18 hours with the following use: 90 time checks, 90 notifications, 45 minutes of app use, and a 30-minute workout with music playback from Apple Watch via Bluetooth, over the course of 18 hours.
Apple Watch is supposed to have 18 hours of battery life, which would translate into a full day if I were to ever keep to a normal sleeping schedule. I was able to lengthen the uptime of my watch to a full 24 hours on days in which I didn't make battery-taxing phone calls with it, or use the half-as-power-hungry heart rate monitor.