Wireless charging is increasingly common in modern smartphones, and there’s even speculation that Apple might ditch charging via a cable entirely in the near future. But the slight convenience of juicing up your phone by plopping it onto a pad rather than plugging it in comes with a surprisingly robust environmental cost. According to new calculations from OneZero and iFixit, wireless charging is drastically less efficient than charging with a cord, so much so that the widespread adoption of this technology could necessitate the construction of dozens of new power plants around the world. (Unless manufacturers find other ways to make up for the energy drain, of course.)
On paper, wireless charging sounds appealing. Just drop a phone down on a charger and it will start charging. There’s no wear and tear on charging ports, and chargers can even be built into furniture. Not all of the energy that comes out of a wall outlet, however, ends up in a phone’s battery. Some of it gets lost in the process as heat.
While this is true of all forms of charging to a certain extent, wireless chargers lose a lot of energy compared to cables. They get even less efficient when the coils in the phone aren’t aligned properly with the coils in the charging pad, a surprisingly common problem.
To get a sense of how much extra power is lost when using wireless charging versus wired charging in the real world, I tested a Pixel 4 using multiple wireless chargers, as well as the standard charging cable that comes with the phone. I used a high-precision power meter that sits between the charging block and the power outlet to measure power consumption.
In my tests, I found that wireless charging used, on average, around 47% more power than a cable.
Charging the phone from completely dead to 100% using a cable took an average of 14.26 watt-hours (Wh). Using a wireless charger took, on average, 21.01 Wh. That comes out to slightly more than 47% more energy for the convenience of not plugging in a cable. In other words, the phone had to work harder, generate more heat, and suck up more energy when wirelessly charging to fill the same size battery.
How the phone was positioned on the charger significantly affected charging efficiency. The flat Yootech charger I tested was difficult to line up properly. Initially I intended to measure power consumption with the coils aligned as well as possible, then intentionally misalign them to detect the difference.
Instead, during one test, I noticed that the phone wasn’t charging. It looked like it was aligned properly, but while trying to fiddle with it, the difference between positions that charged properly and those that didn’t charge at all could be measured in millimeters. Without a visual indicator, it would be impossible to tell. Without careful alignment, this could make the phone take way more energy to charge than necessary or, more annoyingly, not charge at all.
The first test with the Yootech pad — before I figured out how to align the coils properly — took a whopping 25.62 Wh to charge, or 80% more energy than an average cable charge. Hearing about the hypothetical inefficiencies online was one thing, but here I could see how I’d nearly doubled the amount of power it took to charge my phone by setting it down slightly wrong instead of just plugging in a cable.
Google’s official Pixel Stand fared better, likely due to its propped-up design. Since the base of the phone sits flat, the coils can only be misaligned from left to right — circular pads like the Yootech allow for misalignment in any direction. Again, the threshold was a few millimeters of difference tops (as seen below), but the Pixel Stand continued charging while misaligned, albeit slower and using more power. In general, the propped-up design helped align the coils without much fiddling, but it still used an average of 19.8 Wh, or 39% more power, to charge the phone than cables.
On top of this, both wireless chargers independently consumed a small amount of power when no phone was charging at all — around 0.25 watts, which might not sound like much, but over 24 hours it would consume around six watt-hours. A household with multiple wireless chargers left plugged in — say, a charger by the bed, one in the living room, and another in the office — could waste the same amount of power in a day as it would take to fully charge a phone. By contrast, in my testing the normal cable charger did not draw any measurable amount of power.
While wireless charging might use relatively more power than a cable, it’s often written off as negligible. The extra power consumed by charging one phone with wireless charging versus a cable is the equivalent of leaving one extra LED light bulb on for a few hours. It might not even register on your power bill. At scale, however, it can turn into an environmental problem.
“I think in terms of power consumption, for me worrying about how much I’m paying for electricity, I don’t think it’s a factor,” Kyle Wiens, CEO of iFixit, told OneZero. “If all of a sudden, the 3 billion[-plus] smartphones that are in use, if all of them take 50% more power to charge, that adds up to a big amount. So it’s a society-wide issue, not a personal issue.”
To get a frame of reference for scale, iFixit helped me calculate the impact that the kind of excess power drain I experienced could have if every smartphone user on the planet switched to wireless charging — not a likely scenario any time soon, but neither was 3.5 billion people carrying around smartphones, say, 30 years ago.