Upon official release, the Ultra will feature a total battery life of up to 36 hours, with a potential for up to 60 after a later update is introduced in the fall. Apple measured this 36-hour window through the use of 180 notifications, 180 time checks, 90 minutes of app use, and a 60-minute workout with music playing over Bluetooth.
The Apple Watch Ultra is also capable of 28 hours of connection to an iPhone over Bluetooth and eight hours of LTE connection. Apple notes that cellular connections and any workouts going over 60 minutes will deplete the Ultra's battery life far faster.
A battery optimization feature will be debuted in the fall for all watchOS 9 users, according to the company, which will allow the Ultra up to 60 hours of battery life via a Low Power Mode profile. This will disable specific features and limit other programs, like heart health notifications, always-on display, autostarting workouts, and more.