Charging Your Phone Overnight: Battery Myths Debunked (2024)

There are a lot of questions about mobile phone batteries. Should you leave your phone plugged in overnight? Is it bad for the phone? Bad for your safety?

In fact, how much should you charge your phone? When's the right time to plug in? Should you let it run down to zero every time? Should you charge it up to 100%? How do you get the longest life out of the battery inside a phone? Does it even matter, if you're going to keep the handset around for just a couple of years and then upgrade?

This discussion goes well beyond the worry of moderate harm to a device, as some people have fears of "overloading" a phone battery. That worry seems justified, as only a few years ago, Samsung's Galaxy Note 7 smartphones werebursting into flamebecause of battery issues. But as we'veexplained before, unless a device has some serious manufacturing defects (as Samsung's phone did), a fire in your pocket (or on the nightstand) is unlikely.

The problem is that some of the research and opinions out there are diametrically opposed. We've narrowed down the right and wrong things to do as best we can. We present to you the myths and truths of iPhone or Android phone charging, in particular regarding whether you should plug you phone in overnight.

Charging My iPhone Overnight Overloads the Battery: False!

One thing all the experts agree on is that phones are smart enough notlet an overload happen. Extra protective chips inside make sure that can't happen in a tablet, a phone, or even a laptop. Once the internal lithium-ion battery hits 100% of its capacity, charging stops. But if you leave you phone plugged in overnight, it is going to use a bit of energy by constantly trickling new juice to the battery every time it falls to 99%. That is eating into your phone's lifespan (see below).

The Best Thing to Do

Don't worry about this too much. Plug the phone in or place it on the wireless charger when you go to sleep. If you wake up in the night, unplug it or move it to prevent constant trickle-charging. You could also plug your phone into asmart plugthat's on a schedule to turn off.

Potential Problems With Charging Phones Overnight

Trickle charges can generate some heat. Many experts recommend taking a phone out of the case to charge it overnight. But that's not always feasible with a complicated protective case.

At the very least, do not stack anything—books or other devices, for instance—on top of a charging device. And for the love of Jobs, do not put your phone under your pillow. Do any of the above, and you can expect the phone to get hot—not necessarily hot enough for spontaneous combustion but enough to damage the battery (see below).

(Credit: Shutterstock/spyarm)

If you're afraid of fire, some recommendleaving the charging device on a dish or saucerwhile it's plugged in or placing it on something metal that is more likely to dissipate heat, the way a heatsink does on the chips inside a PC.That's not much of an option if you use a wireless charging pad, so don't sweat it.

Bad Cables

If you're charging with a knockoff cable that isn't made by the device's manufacturer or isn't at least "certified" in some way (iPhone Lightning cables should beMFi certified, for example), that could be a problem. The cord and connectors may not be up to spec for your phone or tablet. Don't skimp by buying chintzy cables.

That said, don't think you have to buy chargers made by your phone manufacturer. Most handsets these days support universal standards. One such standard is USB Power Delivery (PD)—all major modern phones from Apple, Samsung, and Google support it. You just need a compatible cable to use between the PD charger and the phone.

I Should Freeze My Phone to Prevent Battery Problems: False!

Lithium-ion batteries hate two things: extreme cold and extreme heat. Repeatedly charging a phone in sub-freezing temps can create a permanent plating of metallic lithium on the battery anode, according toBatteryUniversity. You can't fix that problem; it's simply going to kill the battery faster.

(Credit: iStock/sankai)

Your phone battery is not alone in hating heat; all the internal components of a phone feel the same. Your phone is a computer, and computers and hot air are mortal enemies going back decades. Leave your black-screened phone sitting in the sun as you laze by the pool, but don't be surprised when it throws a warning that it needs to cool off. Instead, give it some shade. In the summer, keep it off the car dashboard.

Apple specifically says charging iPhones in an environment that's hotter than 95 degrees F (35 degrees C) does permanent damage to the battery. Expect the same with any modern phone.

The Best Thing(s) Never to Do

Don't charge a phone when it's too cold or hot. And don't put your phone in the freezer.

My Battery Should Always Drop to Zero Power Before I Charge It: False!

Running a phone until it's dead—a full discharge—isnotthe way to go with modern lithium-ion batteries. Try not to let it get close to 0%. That wears out a lithium-ion battery faster than normal.Partial dischargeis the way to go.

(Credit: GettyImages/Priscila Zambotto)

Batteries are on borrowed time from the get-go. The insides are in a constant state of decay that can't be helped. Over time, the materials inside are simply going to hold less and less power. If you've got an older iPhone still in use and wonder why it's only got a charge for a few hours compared to the almost full day (or two) you got when it was new, that's why. Capacity diminishes over time.

Drain a phone battery to zero only when you want torecalibratethe internal sensor that displays your phone's battery level. Success here is hardly guaranteed—in fact,many people don't think it works at all—but it's recommended by some, especially with a phone that goes down to 10% (or even 20% or 30%), then abruptly dies.

Note that even when you do use the phone all the way to auto-shutdown, that may not mean the battery is actually at 0%. Leave the phone alone for a few hours, if you want to try recalibrating. Then give it a reset for good measure.

The Best Thing to Do:

Plug the phone in before it asks you to enter alow-power mode; iOS will ask you to turn that on when you hit 20% power. Plug the phone in when it's between 30% and 40%. Pull the plug at 80% to 90%; going to full 100% when using a high-voltage charger can put some strain on the battery. Keep the phone's battery charged between 30% and 80% to increase its lifespan.

Apple claims that with fast charging, iPhone batteries can increase 50% in only 30 minutes. Thatrequires a USB-C power adapter, which in turn means using a specialUSB-C-to-Lightning cable or a higher-voltage charger such as the one from an iPad or even a MacBook.

Don't fast-charge your phone if it doesn't support that. It's another thing that'll strain the battery. But it's hard to find a phone these days that doesn't support fast charging. iPhones have all had it (the aforementioned USB PD) since the iPhone 8 came out in 2017.

For more, read Does Fast Charging Ruin Your Phone Battery?

My Battery Develops a 'Memory': False!

Phones developing a "memory" was a problem with oldernickel-cadmium (NiCad) batteries. That's where the whole "discharge the battery entirely" dictum came from. As we've said, that's not necessary with lithium-ion batteries.

So why do lithium-ion batteries not seem to last as long as they age? It's not about "memory": It's aboutcapacity. Over its lifetime, your phone battery degrades enough that in the same amount of charging time, a new phone could hit a full charge, but an older phone might get to only 82% or so.BatteryUniversity calls it "old man syndrome."

(Credit: Shutterstock/Jirsak)

Another way to look at this: Newer batteries are simply hungrier to suck up all that power.

Apple claims that "Apple lithium-ion batteries are designed to hold at least 80% of their original capacity for a high number of charge cycles," but it admits that the amount differs from product to product.

Apple iPhone batteries also support "fast charging," so they'll get to 80% pretty quickly. After 80%, capacity increases more slowly, partly to prevent heat buildup, which extends battery life. But guess what? Fast charging isn't great for a lithium-ion battery, either. It corrodes even faster.

Older iPhones came with a 5-watt charger block. It works, but you can charge faster with a 10W or 12W charger (as you get with an iPad). And the newest iPhones, including the 13 and 14, can charge between 25W to 27W. Apple doesn't even include charger blocks with phones anymore, but the company sells a USB-C power adapter with dual 35W ports for $59. Or you could buy a third-party USB-C charger.

If you use Qi-based wireless charging, keep in mind that most support 7.5W, with wireless fast charging now available. But Apple's MagSafe chargers, available for the last three generations of iPhones, can charge at 15W.

The Best Thing to Do:

Stop worrying about "memory."If you're going to charge overnight, don't fast-charge. Your charger should be lower voltage, such as that 5W charger that came with your pre-2017 phone.

Phone Batteries Last Only a Few Years: False(ish)!

A phone battery measures its lifespan in "charge cycles." That means every time you discharge 100% of the phone's capacity, it's one cycle count. But it doesn't mean you went all the way to zero.

For example, say your phone is at 80%. You go down to 30% (that's half the battery capacity), and you charge it back to 80% and use that 50% up again—that's one cycle. You could use 75% one day, 25% the next; again, that's one cycle. Expect iPhones to have a lifespan of 400 to 500 charge cycles—but again, that's not necessarily that the phone is actually plugged in 400 to 500 times to charge.

If the phone's capacity has eroded enough, you may have to do that 50%-charge-and-use a couple of times a day, and the battery lifespan will go downhill even faster. Here'sApple's graphictrying to explain it:

(Credit: Apple)

While your phone battery doesn't have a "memory" that causes the capacity to shrink, that limited lifespan means you may want to swap in a new battery.

Back in 2017, Apple admitted that itsecretly slowed downbatteries on older iPhones in the name of "overall performance and prolonging the life of...devices." After an uproar, Apple offered battery replacements for these phones at a discount for a while. With "Right to Repair" becoming a bigger deal, in 2022 Apple launched a self-service repair store option that includes battery-change options.

You can try it yourself, but battery replacements are generally best done by a professional. Few new phones have a truly user-swappable battery. Opening up the guts of your phone, even if it doesn't void the warranty, isn't for the faint of heart.

Why are there almost no phones with swappable batteries? Most lithium-ion batteries perform effectively for around two to three years, and that's when the manufacturers would prefer you upgrade to a new phone. Why bother making it easy to swap a battery?

Now that the average phone user in the US keeps a phone for a while—one 2022 survey showed 26% update phones only every two years, a further 28% wait three years, and a quarter even wait four years—there's far less incentive for phone makers to help you keep your phone running; they aren't exactly fans of right-to-repair options.

This situation might get easier in a few years, as the European Union now has a law that forces Apple and other phone makers to manufacture all phones with user-replaceable batteries by 2027.

The Takeaway

If you plan to swap out your phone every year or two, charge it any way you want for as often as you want, and don't worry about diminished capacity. But if you want to stretch out your phone's useful life, pay attention to best practices for lithium-Ion batteries, as described above. Or you could just get a new battery installed every couple of years, which is much cheaper than a brand-new phone. Then hold out for 2027!