Apple’s release notes say the watchOS 7.3.1 update offers a fix for an issue that prevented some Apple Watch Series 5 and SE models from charging after they had entered Power Reserve mode.
watchOS 7.3.1 addresses an issue that prevented some Apple Watch Series 5 and Apple Watch SE devices from charging after entering Power Reserve.
watchOS 7.3.1 can be installed on an Apple Watch Series 5 or an Apple Watch SE via the Watch app on the device’s attached iPhone. Go to “General” -> “Software Update” to install the new software. The Watch should have at least 50% battery life, be connected to a charger, and be in the range of the iPhone.
Today’s update is only available for the Apple Watch Series 5 and the Apple Watch SE. Other Apple Watch models will not show an update as available.