As long as we’ve had smartphones, we’ve wanted to charge them faster. Each year, the newest phones come out with incredible advancements in fast charging technology. Where a 30W charger used to feel incredibly fast to me, it’s now a pretty standard charging speed, replaced by blistering figures over 100W in the fastest phones. I remember a phone from a few years back actually offered 150W charging, capable of charging the phone to 50% in just five minutes. The iPhone 17 Pro Max’s 40W charger can reach a 50% charge in 20 minutes.
But as phone makers experiment with fast charging, I’ve noticed an uptick in concern about overheating and battery damage. Is the device in my pocket just one fast charge away from exploding? In short: probably not, and here’s why.
Why Phone Batteries Lose Charge Capacity Over Time
Ever wonder how a phone actually charges? Lithium-ion batteries (the type used in iPhone and Android devices) have two layers—lithium cobalt oxide and graphite. When lithium ions move from the graphite layer to the lithium cobalt layer through an electrolyte solution, electrons get released. When you charge the battery, the ions move back in the other direction and are stored to be released later, when you power on and use your device.
That release of energy creates the heat you may feel radiating from the back of your phone after a long charging session or heavy use. And, yes, that heat can damage the battery in the long term. However, I feel like I need to stress that li-ion batteries have become smaller and more efficient over the years. They can handle more charge cycles—going from depleted, to full, and back down again—before they begin to lose their charge capacity. For a visual breakdown, I think the below video from tech YouTube channel Branch Education offers a helpful representation.
As your smartphone goes through charge cycle after charge cycle, it degrades naturally. One reason is the electrolyte solution within the battery. Over time, the salts in the solution can crystalize, forming solids that block the transmission of ions through the solution. If fewer ions get through, fewer electrons are released, and the battery can’t provide as much power as it did when it was new.
Ultimately, this process is unavoidable. However, this crystallization can happen more quickly if your phone is exposed to excessive heat, such as funneling a lot of power into the battery at once with a fast charger. The inside of a li-ion cell is a delicate balance that can be disrupted if you put more power into the battery than it’s designed to accept, because it removes too many lithium ions from the internal structure of the battery, permanently altering it. And once that lithium’s gone, you can’t really put it back. However, I should add that the same thing can happen just by leaving it in your car on a hot summer day.
(Credit: Samsung)
How Phones Mitigate Battery Damage
In the early days of fast charging, batteries got very hot when charging quickly. Phones weren’t built to vent excess heat from the battery effectively, so they were more prone to overheating. But guess what? Current phones are now much better at ventilation and don’t have this issue. For instance, phones now have heat shields, thermal layers, and even cooling pipes to move heat away from the battery. I’ve even seen some gaming phones with cooling fans.
Apple’s iPhone has battery optimization settings (Credit: Apple)
Plus, phones are now built with features that manage the flow of power going to the battery during a charge. Your phone will stop taking in power once the battery is full, even if it remains plugged in, which is why I’m not worried about my phone bursting into flames when I charge it overnight. Adaptive charging features also help optimize things by “learning” your behavior so the phone holds off on charging to 100% until closer to when you actually need it. Multi-stage charging means more power is directed into the battery at first, but trickles off as it approaches 100%, so you’re not getting 80W of power the entire time.
Get Our Best Stories!
A Smart, Bold Take on the Wireless World
By clicking Sign Me Up, you confirm you are 16+ and agree to our Terms of Use and Privacy Policy.
Thanks for signing up!
Your subscription has been confirmed. Keep an eye on your inbox!
Manufacturers are also always developing new charging protocols and battery designs to help get more juice to phone batteries in less time. In recent years, Apple has added a collection of battery performance settings and Google is introducing a Battery Health Assistant to its line of Pixel phones that can automatically adjust voltage and charging speeds. More advanced batteries, cables, and power supplies will help manage heat and cut down on any adverse effects, too. So, really, don’t worry about using fast charging.
How to Check Your Phone’s Battery Health
Don’t believe me? Your iPhone should let you check for yourself by showing the current health of your battery, including maximum capacity, if a replacement is recommended, cycle count, and more, under Settings > Battery > Battery Health.
Recommended by Our Editors
Older phones have fewer options, but if you have an iPhone 15 or later running iOS 17.4, I recommend checking Cycle Count, which can help you track how heavily the battery’s capacity has been used up. On iOS 26, you also get a redesigned Battery Settings page with improved battery usage statistics and a new feature to extend battery life.
Android users have fewer options. To see cycle counts, open Settings > About phone > Battery information on Google’s Pixel 8a and later. Samsung users will need the Samsung Members to see cycle counts and other battery health information. If your device isn’t compatible, I recommend using one of several third-party diagnostic apps to find the information you need.
(Credit: Apple)
Should You Use Fast Charging?
So, is fast charging really that bad for your phone? Yes and no. It can be bad for your battery, especially if it goes on for a long period of time at high power. But modern phones are now designed with battery charging management features to make serious damage far less likely. But keep in mind that, as YouTuber Marques Brownlee points out, a lot of these advancements are still too new to know whether they work the way they should in the long term.
Right now, I’m comfortable knowing my phone has features that are supposed to help keep it running as intended. However, I’ll admit that we do ultimately need more data to answer the question definitively, and not just take the manufacturer’s word for it. For now, if you take care of the battery (and follow our advice), this degradation will happen more slowly. Just remember this happens to all li-ion batteries eventually, no matter what you do, so don’t beat yourself up too much over it.
About Our Expert
Experience
John is a writer/photographer currently based in Houston, Texas. He’s written on everything from politics to crypto wallets and worked as a photojournalist covering notable events like the Astros Victory Parade and the Day for Night Music Festival. Current hobbies include learning to shoot 35mm film, building Spotify playlists, and working his way through that menacing TBR stack on the nightstand.
Read Full Bio
