Pleasantly surprised. Though a single example so far, I used 13% battery for a 1:10 hour run (@11% per hour), with backlight (60%) and music on continually, with GPS settings All Systems + Multi Band, and 1-second recording. No Pulse Ox. So, if linear energy drain (an assumption only), then about 9 hours of use in this max energy configuration as compared to the Garmin specifications showing 6.5 hours.
I did experience an overnight drain recently, and have been trying to nail down the cause. Maybe an update? I have not been able to replicate that battery drain. I did reset the watch after that issue.
But my activity (running) usage seems to be very impressive.