Between 2-3 days but the battery life varies by use, configuration, cellular network, signal strength, and many other factors.
To further extend battery, change your Location Update Schedule on your Angel Watch™ app to Manual Mode. This means you'll still be able to check the watch's current location on demand by tapping on the map but the watch will not automatically send its location otherwise. For geo-fencing and to view historic tracking, set the Location Update Schedule to update the watch's location more frequently to constantly refresh its location. Bear in mind this will consume more battery power.