Hi,
Out of the portable mp3 players I sometimes prefer the players that take AAA battery for the power. There are two reasons for it

1) You can power the mp3 player with AAA battery if it runs out of juice and you are in no time/situation to charge the battery if your player is powered by an inbuilt/non-replaceable Li-Ion battery.

2) AAA battery mp3 player can last a lifetime. In case of an inbuilt Li-Ion rechargeable mp3 player the battery eventually stops holding charge and you have to throw the player away once it wears out in 1-2 years

Honestly I love the super convenience of charging the Li-Ion batteries by plugging into the wall rather than removing the AAA battery and charging it on an external AAA battery charger

I am trying to get the best of both worlds.
1) Use an mp3 player that takes rechargeable AAA battery (like Sandisk Sansa m240
or Philips GoGear SA2627/37 . I have one of the above each in my shelf
2) Use rechargeable AAA batteries inside it and recharge them by having it inside the mp3 player and connect it through the USB cord to the computer

Is this possible?

I have seen mp3 CD players that can charge the AA rechargeable batteries inside it when connected to an AC outlet adapter. I hope the same system works for my situation
(eg: Coby MP-CD521 Personal MP3/CD Player with 120-second Anti-Skip Protection
available from jr.com

(# Battery Rechargeable Function (when using optional rechargeable Batteries with optional AC adapter) - Requires 2 x "AA" Batteries (Not Included) / Low Battery Indicator )

If you know any solution to my problem please help by replying
Thanks in advance and I owe you a lot