Fresh from the informative-but-take-it-with-a-grain-of-salt Zune Insider blog comes some juicy details about Zune battery life. According to the insider (Microsoft employee Cesar Menendez), the Zune will get about 14 hours of audio battery life -- not amazing but not bad either. Parameters of the drain: unprotected 128kbps WMA tracks on repeat with default volume, no EQ, and backlight on for 1 second, which is pretty standard (you should be able to play standard MP3s for a while longer).
Cesar later comments that because of DRM processing "Playing music you got from Zune Marketplace will knock down the above battery life, by about 30-60 minutes." Battery life for video or photo playback will be about 4 hours, which seems par for today's course.
Now for the juicy part. Apparently the Zune will last for 13 hours with the WiFi feature turned on. So while it looks like you won't decimate your battery life with WiFi simply turned on, we still don't know what battery life will be like if you "Zune" (ie zap, transfer, beam, or receive) DRM-wrapped music a few times in between charges.
Also gleaned from the comments: the equalizer presets will be: none; acoustic; classical; electronic; hip hop; jazz; pop; and rock, which are the same as the Portable Media Center-powered Toshiba Gigabeat S (the Zune's established cousin). There will be no custom EQ at launch.
Source: Zune Insider