Sorry for the skipped entry in the Carbon Footprint series. My footprint totally died and I had to recharge it for, like, two weeks.
Which brings us to this week's recommendation: battery chargers. Did you know that chargers use power even when the electronic device is not plugged in? In fact, 95% of the energy used by mobile phone chargers is wasted. Why is this? Most electronics these days use batteries, and batteries need direct current for charging. That little black box that blocks the other outlet whenever it's plugged in does not 'know' if the phone is plugged in at the other end; it just goes about its business converting alternating current from the socket into low voltage direct current for your battery. This activity is called a phantom load. This kind of appliance is known in green circles as a vampire.
My AC adapter is rated at 4.8 volts and a 350 mAmp current. That means that fully loaded the phone's battery resistance is almost 14 Ohms. Ohm, my! When the phone is not plugged in, the resistance has to be much lower, especially since the voltage from the wall is 120V, and according to some engineers at Cambridge, a lonely charger sucks a miniscule 0.472 Watts. Even so, according to a CNN article, chargers of all kinds make up fully 5% of your electricity bill every month. Unplugging them is an easy way to cut your bill and your carbon use. Plus, it will be easier to use other devices in the outlet without that bulky plug in the way.
Update 8/19/07: I have altered this column slightly to address concerns of accuracy brought up in the comments below.