The Hidden Costs of Wireless Charging: Efficiency, Environment, and Safety

Wireless charging has become ubiquitous in recent years, with companies like Apple, Samsung and Google all embracing the technology. The benefit is obvious. It's easier to plop a device on a charging pad than it is to wiggle in a USB-C cable.

Despite the convenience, there are some downsides with wireless charging tech. Generally speaking, wireless charging is inefficient, wasting more energy than wired charging. Let's get into the why of it all and detail other risks associated with wireless charging.

How is wireless charging less efficient?

Wireless chargers use more power to completely charge a device, when compared to a cable. A modern smartphone is a great example of this. Charging a smartphone with a wire from zero to 100 percent takes around 15Wh (watt-hours measure the amount of energy needed for a device to run for an hour). The same phone will require around 21Wh (40 percent more) to juice up via a wireless charger, according to a 2020 study by the enterprise platform OneZero. That number could vary based on the charger and how you use it — a 2024 test by iFixit found the energy gap between Apple's MagSafe charger and wired charger to be slightly better at around 36 percent more power used, and also showed how misalignment on a charging pad could halve the efficiency of a wireless charger.

Wireless chargers also generate and waste more heat than wired chargers. Charging pads get pretty hot during use, which is a sure sign of wasted energy.

Is this discrepancy a big deal?

Yes and no. A daily difference of around 6Wh isn't that big of a deal when considering a single wired charger versus a single wireless charger. However, it adds up when considering every wired charger versus every wireless charger. A year of charging up a smartphone with a cable takes around 5.5 kilowatt-hours (kWh) and that shoots up to 7.6kWh with a wireless charger.

Studies have indicated that 30 to 66 percent of smartphone owners use wireless charging pads and related accessories at home, according to the Wireless Power Consortium and the Deloitte Mobile Consumer Survey UK. There are around 7.6 billion smartphones in the world. If 30 percent of those smartphones are being charged wirelessly that would indicate an annual global power waste of 4,830GWh. This amount of energy could power hundreds of thousands of homes for a year. Wireless charging products are becoming more popular every year, so this metric will only go up.

Why is wireless charging less efficient than wired charging?

Wireless chargers transfer power through electromagnetic induction. This is simply not as efficient as a direct charge, as the energy has to go through more steps to be usable. There's also an air gap between the phone and the charger, which lets heat escape.

This is compounded by phone cases and the like, which increase the air gap. All told, wireless chargers lose anywhere from 20 to 30 percent of power throughout the whole process, due to heat dissipation. That's on top of the 5-10 percent of losses that all chargers incur by converting the AC energy coming from an outlet to DC.

Are there any dangers when charging wirelessly?

The heat that wireless chargers produce could degrade your phone's battery over time. Modern phones have safety mechanisms in place to prevent overheating that could seriously degrade your battery or result in a fire hazard. These mechanisms, however useful, will result in your charging session being throttled to a lower speed if the battery reaches high temperatures around the 45C (113F) mark. Make sure to use the charging pad in a well-ventilated area and never put it underneath something like a blanket or pillow.

There are hundreds of chargers out there, and they aren't all created equal. Cheap, unbranded chargers may lack crucial safety features like temperature sensors and foreign object detection. To that end, it can be dangerous to place metal objects between the phone and the charger. Finally, some powerful chargers can interfere with medical devices like pacemakers, as they generate magnetic fields strong enough to trigger the health aide's "magnet mode" and alter the pacing rate.

Is wireless charging bad for the environment?

Wireless charging uses more energy than wired charging, so it has a higher environmental impact than wired charging. Additionally, the charging pads will eventually become electronic waste. The technology's tendency to degrade lithium-ion batteries over time could, in extreme examples, lead consumers to swap out their phones earlier than usual, which would have an additional environmental impact.

Is wireless charging getting more efficient?

Wireless charging is getting more efficient, which is great news. This is due to better coil alignment and industry standards set by MagSafe and Qi2 products. However, it's highly improbable that wireless charging ever catches up to wired charging. A wired connection is simple. It's a plug that goes from point A to point B. Wireless charging requires energy to transmit through magnetic fields.

Are there negatives to wired charging?

Despite some obvious benefits, there are some drawbacks to going with a wired charging solution. Cables degrade over time, and technology changes can force users to upgrade. We all have that cardboard box in the basement filled with dozens and dozens of barely functioning cables of various types. Also, charging ports can wear out after several years of use. Finally, it's just more fun to plop a smartphone on a magical pad, when compared to plugging in a cord.