The Cowon S9 will probably edge out the iPad on battery life slighty for media. Rated 55hrs for continous music playback and 11 hours video. Its an average rating. The iPad is rated around 10hrs(full functionality). Its just an average could be a bit more of less what depending on your settings and what you are doing. I would estimate for continous audio playback the battery life would be quite good on the iPad (40-55 hrs) but it would be silly to just use the iPad as a music device since it lacks portability/mobility to an extent.
10 hrs give or take is what you are probably going to get out of the iPad if you actually use its features. The iPod touch is half that or less. Continous Wifi on the touch I believe is somewhere around 2-3 hours.
