The training app of the Apple Watch uses the heart rate monitor and the GPS, as well as the Bluetooth connection to the iPhone. Of course the training app consumes a lot of battery capacity and therefore the battery life of the Apple Watch is of course shorter.
This could be a problem if the battery of your Apple Watch is already more empty than full, but you still want to stop your activity. Here it makes sense to activate the energy saving mode.
Activating Apple Watch energy saving mode while training application is active
1. Open the Watch App on your iPhone.
2. Scroll down to Training.
3. Switch the slider to "Active" in "Power saving mode during training".
If the power-saving mode is active, the heart rate monitor on the Apple Watch is completely deactivated. However, GPS will still be available for outdoor activities, but will also operate in power save mode.
This means that the battery is no longer so heavily used and the battery of your Apple Watch should last longer.