There are plenty of times our devices are out in the cold. Maybe you’re skiing, and you take your iPhone along with you; maybe you ordered a brand-new tablet for the holidays, and the driver left it on your doorstep. Whatever the reason for your chilled devices, we have an important PSA: If your tech has a lithium-ion battery, and it is in below freezing temperatures, do not charge it.
What happens when you charge a lithium-ion battery below freezing
There are two main issues here. First, charging lithium-ion batteries when they are below freezing permanently reduces their overall capacity. All batteries lose their maximum capacity over time — that’s chemical ageing. However, charging a below-freezing battery will immediately lower its capacity, making it seem like it’s much older than it really is. Who wants a brand-new piece of tech that loses battery power so quickly? No one, is the answer.
Secondly, however, and more importantly, charging a battery in such a condition makes it dangerous to use. Charging a battery below freezing essentially turns it into a ticking time bomb. Quite literally — the battery could eventually explode. While it wouldn’t be necessarily immediate, and a fiery explosion is not guaranteed, that battery is destined to fail at some point in the future.
This information comes to us from an incredibly detailed electrical engineering forum post from user metacollin. The post is an excellent, in-depth explanation of how it all works, including a breakdown of how lithium-ion batteries function in the first place. We encourage you to read their post for all the details. However, here’s a very simplified description, just to wrap our heads around things.
Why lithium-ion batteries can’t be charged below freezing
A lithium-ion battery has two sides — the anode and the cathode. These two sides act like sponges for the lithium ions; when you use the battery, lithium moves from the anode to the cathode. When most of the lithium leaves the anode and rests in the cathode, the battery is “discharged,” and you’ll see your device power down.
When charging, the lithium moves from the cathode back to the anode. When most of the lithium makes it back to the anode, your device is charged up. With me so far?
Now, when you charge a battery below freezing, the anode doesn’t “soak” up the lithium. Instead, the lithium coats the anode. This collection of lithium is quite stressful on the anode, and, as the anode naturally expands during charging, this coated lithium forces its way inside. Hopefully, this issue simply results in a battery that unexpectedly fails; however, the process could result in the anode and cathode coming into contact with each other, which could produce a fire or an explosion.
When can you charge your cold tech?
Now, these issues only happen if you charge a battery in below-freezing temperatures. You can safely charge a “cold” battery, so long as the temperatures are above 0°C.
If you’re waiting for a new iPad, for example, and the driver left it outside of your house on a cold, 38° day, you’re safe to charge it. However, if it is below freezing outside, you’re better off letting the iPad sit in the house for a little while, to make sure the battery warms up enough. The good news? You only have to wait to charge it. Go ahead and power it on! Batteries below freezing are safe to discharge, and, since most tech arrives with some level of battery power, you can still get a head-start setting it up.
Unfortunately, there isn’t much information out there detailing how long it takes for a Lithium-ion battery to warm up to a safe level. It’s likely a good rule of thumb to wait until the device itself doesn’t feel as cold as it did in the freezing temperatures, but, of course, that’s subjective.
Depending on the device, there are ways to check the battery temperature. Android devices can use a third-party app called Ampere to see if their batteries are above freezing. However, many devices don’t have access to these types of apps. You also likely don’t have the tool necessary to both open the device in question and test the battery’s temperature manually.
Our advice, however, is to not overthink it. If it took too long for batteries to safely warm up after being outside, you’d probably hear about this issue a lot more. Instead, you’re better off simply waiting a bit for your device to warm up before plugging it in.