Name: iPhone and Samsung Battery Heat Test: How Hot Is Too Hot?
Uploaded: 2023-08-09T13:00:00Z
Duration: 5 min 35 s
Description: Heat is enemy No. 1 for smartphone batteries and can lead to irreversible damage. But at what temperature will you get a warning? And what can you do to limit the impact? WSJ’s Joanna Stern heated up an iPhone and a Samsung Galaxy S to get the answers. Photo illustration: Nayon Cho for The Wall Street Journal

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Heat is enemy No. 1 for smartphone batteries and can lead to irreversible damage. But at what temperature will you get a warning? And what can you do to limit the impact? WSJ’s Joanna Stern heated up an iPhone and a Samsung Galaxy S to get the answers. Photo illustration: Nayon Cho for The Wall Street Journal

https://m.wsj.net/video/20230809/9ab6a50e-7bd1-4a70-afd6-730a5136be69/1/hls/manifest-hd-wifi.m3u8

iPhone and Samsung Battery Heat Test: How Hot Is Too Hot?

Maybe you've seen this warning lately. It's not good, especially for your phone's battery. And... But how hot is too hot? Action. There was only one way to find out. Put some phones under a food heat lamp, of course. And 137 degrees. And there's the screen. Please do not do this at home for many reasons, but mainly, heat is really bad for your phone's battery. And well, you may have heard.

You know, the heat is not backing off.

And that heat is not going away.

Heat.

Heat.

And combine that environmental heat with processor intensive tasks and even fast charging and the phone temps are only going to rise. So why do batteries hate heat? And what temperature triggers the warning? And is there anything you can do about it? And is having a mini phone fan cool? All right, let's heat up some phones and answer those questions. Okay, first thing to answer, why is heat so bad for batteries? This is a lithium ion battery from inside an iPhone. I'll spare you the chemistry class, but there's a complicated chemical reaction that occurs during charging and discharging. As you increase the temperature, the speed of that chemical reaction also increases, that can cause the battery to drain faster and the actual battery components and capacity to degrade over time. You can check the status of your iPhone or Android phone's battery capacity under settings. But how hot is too hot for a smartphone battery? 95 degrees seems to be the magic number according to Apple and Android phone makers like Samsung. Apple specifically says here that exposing your device to ambient temperatures higher than 95 degrees Fahrenheit can permanently damage battery capacity. But that doesn't mean your smartphone will warn you about overheating at 95 degrees. I decided to test it myself by putting this iPhone 13 Pro and Samsung Galaxy S23 Ultra under a heat lamp. I took the temperature readings with this FLIR thermal camera and an external thermometer as a backup. The first test was just the phone under the fake sun. The alert popped up on the iPhone after baking for seven minutes and 20 seconds, just as the front of the phone's temperature hit 137 degrees. On the Samsung, an alert popped up at the phone was too warm about seven minutes in when it was 128 degrees. But unlike Apple's warning, Samsung's doesn't limit you from using the phone. It just limits usage of some parts of the device. The second test, I wanted to know if fast charging which generates heat on its own would make the temperature rise faster. So I ran the experiment while the phones were charging with this special cord that shows the charging speed. With both the iPhone and the Samsung, the phones just slowed the charging speed as they got warmer. Oh wait, now it's going down the charging speed. Both phones had their alerts pop up around the same temperature, between 130 to 135 degrees. Ow, very hot. Very, very hot. And then there was the final test, recording some video while under the hot sun. This really sped up the heat because recording video is a very processor intensive task. The phone is at about 135 degrees, and with the video playing, it happened in under five minutes. So what can you do about all this? Well, don't put your phone under a heat lamp, but sometimes heat happens. So here are some ideas that I tested. Number one, buy a bag. I bought this $19 thermal bag on Amazon. I put the phones in it and then put it under the light and...

Colleague: Oh, no, it's smoking.

Okay, yeah, it is, it is. The thermal bag hit 302 degrees and we thought, "Let's stop this." The phone totally cool, totally fine inside the thermal bag. The maker of the bag, a company called WALLFID did not respond to my request for comment. I did try this $30 bag from a company called PHOOZY a few days later and it didn't smoke and it kept the phone cool. So yeah, I'd go with that one. Number two, limit fast charging and cases. Apple and Android phone makers use software to balance fast charging with battery longevity. And honestly, I'd say the convenience of charging fast is better than babying your battery. But if you want to slow down, go back to this tiny charging cube if you have an iPhone. Samsung lets you turn off fast charging in settings. Apple also suggests removing phone cases since they can generate excess heat as well. Some Android phones are designed to better handle fast charging though. This OnePlus 10T has a vapor cooling system so it can charge from zero to 100% in 20 minutes. Number three, try a fan. Obviously, that bag doesn't work if you wanna use your phone. So I tried Razer's $60 phone cooler chroma which attaches back here. The only problem with it is that the fan itself needs to be plugged in. Still, I was blown away at how cool it kept the phone. No temperature warning on this side. It has been under the lamp for about 10 minutes. Look, the good news is battery damage isn't gonna just happen from that one time you left the phone on the beach, but your battery is gonna degrade over time and heat will only speed that up. So stay... There's only one place you're going with this phone. It's not a rave, it's a land party.

Everything is now a tech thing. In creative and humorous videos, WSJ senior personal tech columnist Joanna Stern explains and reviews the products, services and trends that are changing our world.