Smartphone maker Nokia estimates most devices need only about two hours to fully charge, making overnight charging highly wasteful; users also should disengage and unplug chargers from the wall when they’re done. Another helpful tip fromBatteryUniversity.com is not to wait until cell phone power is nearly or completely depleted before recharging, because full discharges put a strain on the battery that can shorten its lifespan.

Umbra Fisk, an environmental columnist at Grist.org, advises using a power strip and even a timer as parts of a central charging area for all mobile devices to facilitate monitoring and reduce overcharging. Energy Star-qualified (EnergyStar.gov) cordless phones demand about half the energy of standard units.

Energy Star reports that the average U.S. household spends $100 annually to power devices while they are off, constituting nearly 10 percent of annual electric utility bills and amounting to an annual total of 100 billion-plus kilowatt hours of U.S. electricity consumption and more than $10 billion in annual energy costs.