Dear Tom and Ray:
Oftentimes, I charge my mobile phone or iPod using the cigarette lighter in my car. Does that do any damage to the battery, like limit its life span? If so, should I stop? If not, shouldn't everyone be charging their devices via their cigarette lighter instead of sucking energy out of the power lines where we live? Is car charging a possible "alternative" energy source?
Tom: By jeebers! You've solved the world's energy crisis, Tom!
Ray: Um, not really. The answer is that it's not harmful to charge your devices in the car, but you're ultimately using gasoline to do it.
Tom: The car's battery is an energy-storage device. When you use the battery's energy -- by either starting the car or charging a cell phone -- that energy has to be replenished.
Ray: It gets replenished by the alternator, which converts mechanical energy from the engine into electrical energy -- which is used for doing things like firing your spark plugs, operating your windshield wipers, powering your sound system and recharging your battery.
Tom: And the more energy you draw from the battery, the more gasoline you have to use to charge it back up.
Ray: In the case of charging an iPod, it's not much gasoline. But if you're comparing them, the electrical energy that comes into your house from the power company tends to be cheaper and cleaner than the electrical energy produced by the gasoline engine in your car.
Tom: What we really should have are solar panels built into the roofs, hoods and trunks of our cars. They'd need to be part of the car's surface, so they wouldn't affect the car's aerodynamics and reduce its mileage.
Ray: The Prius has a solar-panel option that runs a fan to keep the car cool when you park in the sun, which is a nice idea, if a bit of a gimmick.
Tom: Unfortunately, with today's solar panels, and the amount of surface area available, you can't generate enough power to move the average car. But if you can run a fan, you certainly can produce enough power to charge cell phones and iPods. Why not?
(Car Talk is a nationally syndicated column by automotive experts (and brothers) Tom and Ray Magliozzi. Write to them at the Car Talk Web site.)