I encode my music at 192VBR so the files are kinda large & therefore put more drain on the battery but
I'm still getting 18-20+ hours of playback! I've got the iRiver v2.51 firmware installed & the files are a combination of mp3's & wma's. Before the replacement, I couldn't get 4 hours of playback - so needless to say, I'm a happy camper!
That daughterboard is a real mother to get out though, at least in my unit - the screws were REAL tight! Make sure you have a small phillips-head screwdriver (with some good torque) to make the change - unless you're lucky enough to remove the battery without taking out the board...