How energy-efficient is your cell-phone charger? (And why have you never thought to ask?) The world’s five biggest cell-phone manufacturers have rated the chargers they sell, from an energy-sucking one star to an eco-friendly five stars. If everyone with a cell phone “switched to a four- or five-star charger,” declares Nokia, “this could save the same amount of energy each year as produced by two medium-sized power plants.”
