I’m thinking of a far future setting for this one, but the hook could probably be adapted for modern or, with some effort, a past/fantasy setting.

Electricity has gone out for the past week in the area the PCs live in. All of their portable devices (cell phones, PDAs, laptops, computers, etc.) are running low on battery juice, and their fully electrical cars are out of charge. Chaos is rapidly descending on the area as everyone else is in the same predicament. The PCs are hired by the local officials to investigate the cause of the blackout and to bring it to an end. They have to do so without much of their technology in hand, or they have to scrounge up enough battery power to keep their devices running. If their cybernetic implants run off of batteries that recharge from the local power grid, they’re also in for a world of hurt as their implants begin to fail.