Engadget has the battery life reports for the new Zune 2 players. Generally the new players have increased it both for audio and video use for about 50%. Their battery also charges quite fast up to the 90% charge level. There are still details missing for uses with Wifi ON or with the AC charger. Read the available info up to now below. EDIT: The official report is different than this..
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EDIT (Oct 16): Here are the official data about the Zune 4, 8 and 80 player' battery life. The information Engadget had, wasn't correct.
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Zune 80
Battery life: 20 hours music (WiFi off) / 5 hours video
Battery recharge time: 2.25 hours / 1.25 hour to 90% via USB
Zune 4 / Zune 8
Battery life: 20 hours music (WiFi off) / 4 hours video
Battery recharge time: 2.5 hours / 1.5 hours to 90% via USB
Microsoft hasn't announced details about the battery life, only that it is going to be more than Zune 30. Engadget has these details from Amazon.
[via Engadget ]