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Q. Dear Umbra,

I know it’s supposed to be bad to leave your cell phone charger plugged in when it’s not charging, but here’s something I find myself wondering often: Is it as bad to leave it plugged in with your phone attached after it’s been charged? And what about my laptop charger? Does that leak energy? Can’t remember if you’ve covered this before.

Oakland, Calif.

A. Dearest T.G.,

I have indeed covered some of this before, once or twice, but your question is timely: Just last month, your fine state adopted new energy-efficiency rules for chargers, citing potential residential and commercial savings of $306 million a year. Also, I am all zinged up by your question about leaving chargers attached to gadgets when their job is done — an important, but often overlooked, variable in this multi-pronged energy equation.

First, a refresher on things that plug in, which allows us to bandy about two fun terms. “Vampires” are appliances that suck energy even when you think they’re shut off, like microwaves, DVRs, TVs, and game systems. Anything with a cute little light or digital clock on it is drawing power, usually unnecessarily, and costing you money — one estimate from Cornell University suggests these vampires cost an average household $200 per year. Unplug these items when you’re finished with them, or better yet, use a power strip.