In my battery test, I turn off all power-saving features, leave the Wi-Fi network on, crank up the screen to 100% brightness, and play a continuous loop of music.
In our standard video test (running an MPEG4 video clip on loop, WiFi on, screen at roughly 65 percent brightness), the iPad 2 managed an astonishing 10 hours and 26 minutes of non-stop playback.