Ok, we've finished testing the battery life, and this is what we found:
Zune 4GB and Zune 8GB
Audio: up to 24 hours
Video: up to 4 hours
Zune 80
Audio: up to 30 hours
Video: up to 4 hours
We 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.
Hope everybody had a great weekend!