Am I draining the battery with my headlights?

Dear Car Talk

Dear Car Talk | Jul 01, 2005

Dear Tom and Ray:

I have a '96 Ford Windstar. When I go to the convenience store in the winter, my wife and daughter usually wait in the car. Because it's cold out, I leave the heater on to keep them warm. One time, my father-in-law was waiting in the car with them. It was nighttime, so not only did I leave the car running, but I left the headlights on. When I came out, I got a speech from him about how leaving the lights on when the car is only idling will greatly shorten the life of the battery. I didn't believe him, but not wanting to start a fight, I went along with him and pretended it was a good idea. Is he right? -- Eric

TOM: Well, let me say first, Eric, that you are a man of great perspicacity. You did exactly the right thing.

RAY: Right: You pretended your knucklehead father-in-law was right, and went along with his harmless suggestion in order to keep the peace. If only there were more international leaders with your wisdom.

TOM: To answer your technical question, your father-in-law is completely nuts. Virtually all modern charging systems are equipped to run the headlights without using any electricity from the battery. The engine will use a tiny bit more gas because the alternator is working a little harder. But it's practically immeasurable.

RAY: And besides, shining the headlights into the window of the convenience store helps you see the labels on the beer bottles in the store refrigerator so you don't accidentally take home a six-pack of Panther Pee Light.

TOM: So, when the old man is around, do him the kindness of turning off the headlights when you're parking in idle. It'll make him feel useful and respected. That's important. Remember, he can still change his will!

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