ZuneInsider posted the official Zune 2 players battery specs: Zune 4 & 8 for audio will work up to 24 hours and for video up to 4 hours. Zune 80: for audio up to 30 hours and for video up to 4 hours. The specs are similar to what iPods have and differ from the numbers found from Engadget via Amazon some days ago...
From ZuneInsider :
Zune 4GB and Zune 8GB
Audio: up to 24 hours
Video: up to 4 hoursZune 80
Audio: up to 30 hours
Video: up to 4 hoursWe did all testing using pre-production hardware and software, with the wireless turned off. Audio was tested using 128kbps .wma tracks, and video was tested using 500kbps .wmv videos.
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Zune 2 battery life reports (the previous report from Engadget)