|Griffin's PowerBlock Reserves($40) for your iPhone. It looks like your another battery, a detachable Reserve battery pack. While you're charging your player's internal battery, you're also charging the detachable Reserve battery pack for your iPod or iPhone.
"PowerBlock is our best-selling AC charger/adapter for USB-rechargeable devices, including iPod, iPhone, and other phones and MP3 players. PowerBlock works in almost any AC wall socket, with electrical service from 100 to 240 volts, and delivers safe power levels for iPod, iPhone, MP3 players, and other USB devices. Take the detachable battery pack with you (it's small enough to fit in your jeans pocket). The Reserve battery snaps into your iPod or iPhone's Dock Connector, adding hours of additional time on your iPod or iPhone."