I see see so many posts here about rockbox.  What is rockbox?  And will e130 or e140 use it?  Also are 130 and 140 the only ones that use AAA battery and if not will they also use rockbox?

Rockbox is an alternate firmware.  IN a sense, Rockbox is to mp3 players as Linux is to PC’s.

For information, including what players it runs on, see

For Sansa players with AAA cells, it looks like the M200 series is a work in progress.