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It Costs Around Two Cups Of Coffee To Leave Your Phone Charging All Night

January 19, 2015 - Written By David Steele

For many, one of the biggest differences going from a feature phone to a smartphone was the need to top up battery on a daily basis. Thankfully, modern smartphones are significantly more power efficient than older models and some users can stretch their smartphone battery further, often stepping into a few days, but there are still a great many people who give their device a nighttime charge whilst they’re sleeping. It’s easy to understand why: when we sleep, we don’t use our devices.

However, supposing we require seven hours of sleep but our devices only need two hours to recharged? The charger isn’t idle for those five hours, instead it’s using energy. How much is it using and how much does this cost us? A study started in 2012 by the Lawrence Berkeley National Laboratory found that an average idle charger drew 0.26 watts, up to 3.68 watts when a phone is attached and charging. Crucially, when the phone is charged this falls to 2.24 watts when the phone is attached and fully charged. We can expect these figures to widen as manufacturers improve their chargers consumption at idle, but make ever more powerful chargers that must deliver more current for quicker charging of the ever-increasing battery size in our smartphones. To put this wattage into perspective, it costs about the same as two typical cups of coffee a year. It’s not much, but one hundred and twenty million cups of java a year starts to sound more significant!

This survey excluded wireless (mostly Qi standard) chargers, which are much less efficient than conventional chargers. It also excluded the handy portable chargers, which we can use to top up our smartphones: these are also less efficient than a direct mains charger as there are more energy losses involved here. And there is another issue, which is that Lithium Ion batteries have a shortened lifetime if they are kept fully charged. Mobile chargers switch to a trickle charge, that is they slowly cycle on and off as the battery goes to 100% and then drops back down again. Keeping the battery at or close to 100% charge will bring forward the time when the battery is exhausted and should be recycled; instead the preferred battery management technique is to use it little and often, matched with little charging stints. Of course, this is not possible for many smartphone users. There are technologies that are being pulled together to improve power management, such as using our movement to keep the battery topped up through to engineering and chemical changes to batteries in order to improve their lifetime. Not to mention improvements in hardware and software designed to reduce power consumption.

Meanwhile, we can save money by not putting our devices on charge overnight. For many people, it’s convenient to do this because we otherwise feel too busy. One trick that I’ve started doing is to put my smartphone on charge in the evening before starting dinner. After all, I can’t easily use it when preparing, eating and tidying up, right? This solution isn’t right for everybody but has other practical benefits – it ensures I have some conscious, disconnected time in my day, and some real face to face conversation. Other alternatives include topping up the battery when I am in the car or when I am working at a computer and there’s a handy free USB port. Let us know how you charge up your battery in the comments below.