A Pennsylvania start-up says it has the answer to one of the biggest problems in mobile phones: battery life. After three years of keeping its technology under close guard, Powercast has come to CES 2007 to get consumer and manufacturer attention. Powercast is a radio frequency that is transmitted over a small area, and its energy is "harvested"--wirelessly--to give power to small devices like cell phones. While it's presented as wireless power, Powercast isn't just a replacement for a universal charger. Instead, it's meant to either continuously charge a battery or replace the need for them altogether. It works like...