Though it falls into the "accessory to an accessory" category, Ivyskin's BatteryPack for Quattro 4 SmartCase ($45) finishes what the Quattro 4 started back in September, serving as a slide-on 1700mAh battery for the iPhone 4 that integrates with the earlier $45 plastic, glass, and rubber case. A five-LED power indicator, pass-throughs for speaker and microphone features, and mini USB charging port are on the BatteryPack's back and bottom; holding…
