Amazon is selling the EnerG Slim-Fit Extended Rechargeable iPhone Battery Case for only $29.99 shipped, originally priced at $69.99. This accessory provides 10 extra hours internet use, 12 extra hours of video playback, 13 extra hours of talk time, or 40 extra hours of music playback. Product page. Video after the break.

Great as a back-up, or as a permanent solution ; on/off button for optional power output control. Sleek, low-profile design; rechargeable up to 1000 times – charges through usb cable or iphone 3g and 3gs ac and dc adapters.

[via Amazon]