After the release of watchOS 4.1 Apple, I updated the Watch Series 3 battery page on the official website. The fact is that this update significantly improved the battery life, so that the old numbers became irrelevant.
If in the mode of playing music from the internal storage of the watch itself Apple Watch 3 can work for 10 hours, then when broadcasting tracks via LTE from Apple Music hours will live a little less – 7 hours. But when listening to the radio through the same LTE battery Apple Watch, you can plant it in 5 hours. It's about the new Radio app introduced in watchOS 4.1. It provides access to Beats 1 and other Apple Music stations.
When using the Watch Series 3 during your workout, count on only 3 hours until the watch runs out. This applies to maximum downloads: App Workout, music streaming, GPS and LTE. Do you like to train in silence? This will save you an hour of battery life.
Apple also clarified that the above parameters may change depending on other running applications, settings, type of mobile connection and signal quality, sound quality settings, etc.