Apple start rolling out the watchOS 5.1.3 update With Bug Fixes and Performance Improvements Apple, today released watchOS 5.1.3, the fourth update to the watchOS 5 operating system, that runs on modern Apple Watch models. watchOS 5.1.3, comes more than a month after the release of watchOS 5.1.2, a major update that brought ECG functionality. watchOS 5.1.3, can be downloaded for free through the dedicated Apple Watch app on the iPhone, by going to General, and Software Update. To install the new software, the Apple Watch needs to have at least 50 percent battery