Is It Safe to Leave a Smartphone on a Wireless Charger?

Is It Safe to Leave a Smartphone on a Wireless Charger?

If you’re not well-versed in the complexities of smartphone electronics (like me), you may not fully understand the dos and don’ts of using a wireless charger.  This becomes even more complicated when you’re flooded with myths on the internet about how you should charge your device in the most effective, safest, and least battery-draining manner.

There’s no point repeating junk science so I’ll try to provide as much sourcing as I can for my battery-related statements.

Generally speaking, I would think that your device shouldn’t have an issue popping on and off a wireless charging pad multiple times per day. Though the technology is different than a wired charger—by using a coil to create an electromagnetic field, which itself creates current in a receiver coil—the end result is the same as far as your battery is concerned.

If you aren’t worried about plugging in your phone multiple times a day via its wired cable, you probably shouldn’t worry about how much it’s playing trampoline with your wireless charging pad.

However, this conversation now takes us down the complicated path of smartphone power cycles, which everyone seems to have varying opinions about.

What do the experts say about smartphone wireless chargers?

First, it’s possible that placing your smartphone on a charging pad all day long might strain your battery more than if you let it idle at a lower battery state. As Wired’s Matt Reynolds wrote last year:

“Charging your phone so it stays at 100 per cent overnight isn’t great news for the battery, but that’s not because you’re cramming in more charge than it can handle. A ‘trickle charge’ mechanism cuts off the charger after the phone has reached 100 per cent charge, and only tops up the battery when it drops down a little.

The problem is that you’re keeping the charge level at 100 per cent which, as we know from the previous myth, puts the battery under a certain amount of strain.”

That said, University of Cambridge researcher Kent Griffith goes on to note in the article that your smartphone battery’s manufacturer has set limits to prevent your constant need to charge your phone from harming the battery. Keeping your smartphone “topped off” all the time isn’t “good,” he says, but it shouldn’t hurt your device. In other words, obsess over charging your device at your own risk, but you probably aren’t sacrificing much.

As Lucas Mearian wrote in an article for Computerworld last year, there’s still plenty of debate over how you should approach smartphone charging—especially wireless charging.

One expert in his article claims you should keep your smartphone around 45-55 per cent charged to get the most life out of your battery, which seems ludicrous to me, since you’d barely be able to use your smartphone for a regular day.

Another technology journalist claimed that wireless charging wrecked his iPhone, because it allegedly exhausted its charging cycles faster than if he used a wireless charger. But according to Menno Treffers, chairman of the Wireless Power Consortium, “…by continually topping off the phone battery during the day, as you might do with wireless charging, and not letting your phone battery dip below 50%, you will actually increase the lifespan of your battery.”

Got it? Don’t top it off, but also don’t let it get too low. Let’s continue. Here’s another article from Digital Trends’ Simon Hill, published last year:

“Electrical energy is changed into chemical energy during charging and the reverse happens during discharge,” Dr. Daniel Abraham, senior scientist at the Argonne Laboratory, told Digital Trends.

The battery manufacturer decides how much energy can be stored in the cell, and that determines how much energy you have available to use.

“The manufacturer decides the upper cut off voltage and the lower cut off voltage, which are fixed, and cells cycle between the two voltage ranges,” Dr. Abraham explained. “As long as you choose the voltage range appropriately, you can cycle the cell thousands of times.”

“It doesn’t matter if you have a wireless or wired charger.”

It’s not possible to exceed these limits by leaving your phone on the wireless charging pad for too long, or by leaving it plugged in overnight. You also can’t drain the cell beyond the lower cut off limit dictated by the manufacturer. These limits don’t distinguish between power sources.

“It doesn’t matter if you have a wireless or wired charger,” Dr. Abraham said. “You won’t be able to overcharge or over-discharge a cell.”

Hill also touched on the whole power cycling issue I previously mentioned, and noted that the best way to ensure you aren’t using up more of your device’s limited battery cycles needlessly, you should take a good look at which apps are running in the background on your device. That will probably have more of an impact on your overall battery life than using your wireless charger more than you think is normal.

As well, make sure your wireless charger isn’t located, say, in front of a window. Heat will affect your smartphone’s overall battery life. While it might get a little warm from the wireless charging, it’ll get a lot worse if you’re letting it charge and tan.

So where does that leave us? Here are the key takeaways, from what I gather:

  • You’ll probably do the best for your smartphone’s battery if you leave it charged between 50 to 80 per cent full. You can keep it higher, which might affect its lifespan. You can drain the battery lower, but you’ll start using up more of your battery’s power cycles when you do.
  • Leaving your smartphone on its wireless charging pad won’t destroy the battery. It might have some kind of an effect on its lifespan, but there are other things that are much worse.
  • Make sure you’re getting a reputable charging pad—not some sketchy Amazon knockoff—as an overheating pad (and overheating device) could potentially affect your battery life… and who knows what else.
  • Don’t let your smartphone charge in the sun, whether that’s on your desk, on a long car trip, et cetera.
  • Get rid of apps you don’t need / don’t let apps run in the background for no reason.

My personal experience using a wireless charger for my iPhones

If you don’t mind my sharing a personal anecdote, I’ve been using a wireless charger exclusively with my last two iPhones. I haven’t had any issue keeping said smartphones on said chargers overnight, where they drink up the sweet, electric juice for anywhere from six to eight hours a day. And my Pixel 3 XL sits on a wireless charger almost all day long; no catastrophic battery issues to report there.

The second iPhone I purchased, an iPhone X, was only charged via an antiquated wire before I got my hands on it. If anything, I notice that it’s battery isn’t as solid as a brand-new model, but that’s likely due to how much its previous owner used the smartphone.

Since then, I’ve been charging it wirelessly, and haven’t noticed any tremendous drops in battery life. Those I’ve experienced are gradual enough that I’d chalk them up to, again, how much I use the smartphone, rather than how it gets put to bed each night.


This article has been updated since its original publication.


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