Apple released the watchOS 9 developer preview Beta 2 update. According to the watchOS 9 release notes, Apple is adding a new recalibration feature to the Apple Watch Series 4 and Apple Watch Series 5 with watchOS 9. Recalibration will allow users to more accurately estimate maximum battery capacity.
After updating to watchOS 9, an Apple Watch Series 4 or Series 5 will recalibrate and more accurately estimate its maximum battery capacity.”
After the watchOS 9 updates, Apple Watch Series 4 and Series 5 users will be able to better understand the battery life of their devices. Apple previously introduced a recalibration feature for the iPhone 11 to make iPhone battery life estimates more accurate.
The Apple Watch recalibration process takes place during the update and is completed after installation.