True to the rumors, Apple Watch comes with a special Power Reserve mode that will lightly sip on juice so your watch can keep ticking.
Tim Cook didn’t specify how long Apple Watch’s ‘all day’ battery lasts, but Apple’s website specifies you could potentially keep your watch alive for an extra 72 hours in Power Reserve mode.
If your battery gets too low, Apple Watch automatically switches into Power Reserve mode so you can continue to see the time for up to 72 hours. Testing conducted by Apple in March 2015 using preproduction Apple Watch and software with 4 time checks (4 seconds each) per hour. Battery life varies by use, configuration, and many other factors; actual results will vary.”
You should be able to get 18 hours of battery from your Apple Watch. According to Apple’s tests, that includes 90 time checks, 90 notifications, 45 minutes of app use, a 30-minute work with music playback from Apple Watch via Bluetooth.
Talk Time clocks in around 3 hours with the battery, while audio playback lasts for 6.5 hours. If you just want to use it during workouts it should last for 7 hours straight.
Charging your Apple Watch from zero – 100% will take 2.5 hours based on Apple’s tests, or 1.5 hours to reach 80%.
Interestingly, Apple says that a “42mm Apple Watch typically experiences longer battery life.”