One of the biggest doubts over the Apple Watch is how long the battery inside the device will really last. Clearly conscious of fears that the Watch will keel over before you do of an evening, Apple has published precise details of how long you can expect the battery to last when performing different tasks.
Apple's Tim Cook said in his keynote speech that "most people" could expect to get 18 hours of usage out of the Watch. The Apple website puts a little more flesh on the bones of what this actually means. The company says that 18 hours comprises of "90 time checks [the screen isn't on permanently to save battery life], 90 notifications, 45 minutes of app use, and a 30-minute workout with music playback from Apple Watch via Bluetooth". Given that tech companies often quote figures for the lightest possible usage when stating battery life, it seems Apple is admirably quoting a realistic usage scenario.
Apple has also quoted a series of other battery life figures for various tasks you can perform with the Apple Watch. The company claims the device will offer three hours of talktime for making phone calls when paired with an iPhone. If you're playing music from an Apple Watch via a Bluetooth connection, Apple says you can expect 6.5 hours of battery life - although we can't think of any good reason why you would do this from the Watch instead of an iPhone.
If you're going on a "workout session" which uses the heart rate sensor, Apple says you will get seven hours of battery life from the watch - which should be plenty for anyone bar Iron Man contestants. At the other end of the scale, if you're planning to use the Watch purely as a timepiece (which is the ultimate sledgehammer to crack a walnut scenario), you will get a whole two days of battery life. That rather curiously assumes you're checking the time five times an hour, which seems a tad over-zealous.
Finally, if your Apple Watch battery gets "too low", the device lapses into Power Reserve mode, which lets you continue to see the time for a further 72 hours, but presumably do absolutely nothing else. Not so much a smartwatch, then, but more of a watch...
Apple stresses that all of these tests were conducted using pre-production software, and that your mileage may vary depending on the model of the Watch used and the apps installed. In other words, take all of the above with a pinch full of sodium chloride.