You may have different chargers for your smartphone, laptop, tablet, and other devices. Wondering how much it costs you to leave your charger plugged in? How much power and money are you going to save every year if you diligently unplug your chargers after charging your devices? To answer that question, Chris Hoffman of HowToGeek tested it in real-life conditions using a Kill a Watt meter.

What Happens When You Leave Your Chargers Plugged In?

No charger draws a detectable amount of vampire power

Simply plug the Kill a Watt meter into an electrical socket and then plug your device into the meter. Sitting between the two, the meter measures electricity usage of your appliances and devices. Hoffman used chargers for the iPhone, iPad, MacBook, Android phones and tablets, Windows laptop, Chromebook, and Nintendo 3DS. Surprisingly, not a single charger sucked a detectable amount of vampire power.

Each charger rang up a big fat 0.0 watts of electricity. That doesn’t mean the chargers were not drawing any power. Though the meter showed each charger using 0 watts, it was entirely possible that they were using at least a fraction of a watt, which would be detectable at some point. So, Hoffman tested it in a different way.

The cost of keeping six chargers plugged in for an entire year

He plugged a power strip into the Kill a Watt meter, and plugged several chargers into the power strip. The power strip showed 0.0 watts at the time of plugging it in. Only after plugging six separate chargers in the power strip, the meter registered a measurable reading of 0.3 watts. So, the total vampire power of an iPhone 6 charger, an iPad Air charger, a Chromebook charger, a Surface Pro 2 charger, a MacBook Air charger, and a Nexus 7 charger was a paltry 0.3 watts.

Assuming you leave all these chargers plugged in 24 hours a day, 365 days a year, the total vampire power draw would be 2.628 kilowatt hours (kWh) in 8760 hours over an entire year. The average cost of electricity in the US is 12.98 cents per kWh, according to the US Energy Information administration. It means keeping all the six chargers plugged in for an entire year would cost you just 34.1 cents for 2.628 kWh.