There's no denying it: the MP3 player market is in free fall, and competitors often have to either go big or go home if they want to justify their work over the many smartphone alternatives. Cowon is still kicking, and the extreme battery life of its new D20 player may be a good explanation as to why. Along with 13 hours of video, it can play 90 hours of music on a charge -- enough that the tunes could blast non-stop through a long weekend. Not that the player will