We've been playing with PhoneSuit's Primo micro battery pack on our iPhone 3GS for a few days. As the name suggests, this thumb-sized battery is the smallest we've seen in its class, but somehow it still packs 800mAh of juice -- almost two-thirds of the iPhone's built-in cell. Feature-wise you'll only find battery level and charge status indicators on the front, and a mini-USB port on the back for charging. Unlike the slot-in case-style battery packs for the iPhone, this battery pack's dock connector is on a flat top, which makes it compatible with "all iPhones and most iPods." We also noticed a 2mm gap when plugged in, and apparently this is to allow space for your iPod's /
