In March this year, this article at ZDNet suggested that wirelessly charging your iPhone 8/X will wear out its battery faster than charging with wires. Unfortunately, this article is technically incorrect. But how can this actual experience be explained?
The basis of that article is,
The issue is that when the iPhone is being charged using a cable, the phone is being powered by the cord (there is some load on the battery, but it’s minimal), but when using wireless charging, the battery is what’s powering the iPhone, with the wireless charger only being used to top up the battery. This means that by switching from a cable to a wireless charger, my battery isn’t getting a break, and in turn, this is making me go through recharge cycles at an even faster rate.
Adrian, the author of that article, believed that when an iPhone is charged wirelessly, the battery is providing all the power to the iPhone. This belief is incorrect because the laws of physics dictate that it is impossible to charge and discharge a battery simultaneously. The fact is, when your device is being wirelessly charged, the device is still being powered by the charger. Menno Treffers, chairman of the Wireless Power Consortium told Digital Trends that,
A phone’s battery is not drained when you use it while charging wirelessly. This is a misunderstanding.
Now that we have the facts, how do you explain Adrian’s experience?
The problem lies in the efficiency of wireless chargers. For wired charging, the efficiency is close to 100 per cent. If the wired charger provides 5W of power, the device will receive almost all the 5W of power. For wireless chargers, the efficiency is far less than 100 per cent. Typically, it can be at say 72%. So, what happened is that when the wireless charger receives and transmits 5W of power, only 3.6W will be received by the device and the rest is wasted as heat. That’s why for the same power provided (5W), wireless charging is slower than wired charging.
Since the iPhone 8/X does not support fast wireless charging, wireless chargers can only operate at 5W. When the iPhone is in sleep mode, it typically draws in very little power. But when you use the iPhone intensively, it can draw power at close to 5W.
Here lies the crux of the problem.
Since a wireless charger is inefficient, it can only provide say 3.6W of power. But if the iPhone requires, say 4.5W of power, the wireless charger is not going to provide enough of it. Therefore, all the 3.6W of power from the wireless charger will be consumed by the iPhone, leaving none to charge the battery. Yet, there is still a shortfall of 0.9W of power that the wireless charger cannot provide. So, that 0.9W has to be drawn from the battery. As a result, this hypothetical 0.9W load on the battery is the culprit for the alarming consumption of Adrian’s iPhone battery cycles.
For devices that support fast charging (e.g. some of the Samsung phones), this problem will not exist. That’s because, despite the inefficiency of wireless charging, fast wireless chargers provide far more power (say at 15W) than is needed by the device. Therefore, there will be no need to draw the load from the battery to make up any shortfall when the device is being used.
So, what can you do to prevent your wireless charger from wearing out your iPhone battery?
First and foremost, it is important that you use the right wireless charger. From iOS 11.2 onwards, iPhones can wirelessly charge faster at 7.5W. At such a higher power output rate, your iPhone will not consume more power than the wireless charger can provide. This will eliminate the need for the battery to provide backup power in the event of a power shortfall, thus reducing the consumption of the battery charge cycle.
However, not all wireless chargers can provide 7.5W of power to iPhones. Some chargers that can provide 15W of power to other devices (e.g. the Samsung smartphones) can only provide 5W of power to iPhones. You need to make sure that your fast wireless charger is optimised for iPhones. For this, I recommend mophie – Wireless Charge Pad
