Well, again running Rockbox (open source firmware) I routinely get 13+ hours on 4 1850mAh batteries. It is not unheard of to get over 15 hours on 4 of the newer 2100mAh batteries. My batteries are just the duracell recharbales that I got for $.79 a piece. You are right, the Archos is bigger, and you are unable to take off the bumpers, but I have dropped it numerous times (even while in-line skating) and they really do protect the device. But my Archos is OVER 3 years old. You can also buy an Archos for well under $200.

Many people are choosing between the Zen, the ipod, and the Karma, and if this was your field, then the Karma is by far the thickest and the least pocketable.