Some time ago I purchased a 2GB 1.8LCD player from a local auction site. The image used on the auction showed a nice silver finished player with really nice looking firmware.
What I got delivered was a plain looking white player with possibly the nastiest firmware I have seen, but such is the risk when buying from online auctions. At least it was a true 2GB. Not to fussed on the player I took it's 400mAh battery and used it to replace the 280mAh battery that was in my favourite player which extended it's play time from 5 - 6 hours to 10 - 11 hours.
I recently decided to bring the white player back from the dead, I modded the firmware a bit giving it new menus etc to make it more appealing and then went looking for a new battery for it.
The one thing it was not short of was battery space so I bought an 850mAh iPod 3rd Gen replacement battery (18.00 NZD including delivery) and soldered it in.
Charged it for 3 hours loaded it with 1.9 GB of 128kbps mp3's, set the volume to 15 (half) and started playing on repeat all. I ended up getting a whopping 18 hours continuous play before the player died. I think with a 4 hour recharge I can possibly extend the playtime to 20+ hours.
Will let you know.
I am also currently testing a ($15.00) external USB battery pack (4xAA) on another player. It has been running non-stop now for 28 hours ...... will keep you posted.