Sonic Blue S50 is a portable digital audio player for MP3 and WMA formats. It comes with 128 MB of built-in memory, expandable with external memory cards. It features a rechargeable battery and an integrated FM tuner. You can use the device while it is charging, so you can rip your CDs and load your music while you wait. You can also use a regular AA-size alkaline battery to run the player, but never attempt to charge a non-rechargeable alkaline battery. The player has a backlit LCD display and a user-friendly interface.