What should you know about charging your EV in cold weather?

Charging an electric vehicle is an unfortunate fact of life if you want to enter the emissions-free lifestyle. Whether you're trying to save the planet or just save money on gas, EVs can do that, but only after they've spent a few minutes or even hours plugged into a charger.

Typically, charging your EV isn't a particularly complicated thing. Charging takes more or less time depending on the speed of your charger and the maximum rate of your car, but there's another crucial factor that many people overlook: temperature.

Charging in cold weather, particularly high-speed or DC charging, adds another variable that can dramatically increase the charging rate of any EV. The speed reduction can be incredibly frustrating,for a variety of reasons. 

For one thing, EVs tend to have less range when it's cold, so they'll need to charge more often. That right there is a big problem.

But charging an EV in cold weather can also be frustrating simply because it's cold. You have to stand in the cold, connect a bulky plug, and in some cases fiddle with your smartphone to start the charge, all while the wind and snow slowly turn your fingers into icicles. 

Here's a guide that explains everything you need to know about EV charging in cold weather, how you can make it happen more quickly, and even less painfully.

Before we can delve into the details of charging an EV in cold weather and even situations that might make an EV not charge in cold weather, we need to establish just what the heck is happening when you charge an EV in the first place.

To get that, we need to understand how EV batteries work. While the battery packs that make up the floor of your average electric car are substantially more advanced than those sitting in your smartphone or smartwatch, conceptually, they work in the same way.

A battery is simply two conductive surfaces separated by a non-conductive substance called an electrolyte. One surface, the cathode, is positively charged, which, from an electrical standpoint, means that it's gaining electrons as part of the battery's normal chemical reaction. The other surface, the anode, is negatively charged, meaning it's supplying those electrons. 

The conductive structure of a battery creates a circuit from the anode to the cathode, but since they're separated by that non-conductive electrolyte, where does the power come from? That comes from the flow of ions, which travel through the electrolyte. Electrons catch a ride on those ions, and it's the flow of electrons that moves your car.

It's complicated for sure, but if nothing else, it's important to know that this is a chemical reaction. Those ions literally travel through an electrolyte that is in most cases a liquid, carrying those electrons along, which provide the power to turn the electric motor and make the car go.

When it comes to recharging that battery, the process flows in reverse. A charge is sent into the battery, which causes those ions to pack it up and head back to the anode. They carry those electrons back with them, which are stored up for your next morning school run. 

As mentioned above, electron-carrying ions physically move through a liquid electrolyte solution to make a battery work, whether they're charging or discharging.

Again, this is a chemical reaction, and chemical reactions can speed up or slow down based on many environmental factors. Temperature is the most significant one. 

Just like you move a little more slowly in the morning when it's particularly cold out, those ions can take a little longer to get from anode to cathode as the temperature drops. In extreme cases, that electrolyte solution in the middle can freeze, which literally stops the party cold.

Different battery designs facilitate different temperature ranges, but according to recent research into battery management systems by researchers at SETU in Ireland, the optimal range for a typical, lithium-ion battery pack is between 15 and 35 degrees Celsius. In Fahrenheit, that's about 60 degrees up to 90. It's not a particularly wide window. 

Coincidentally, those temperatures more or less correspond to the range that most human beings find comfortable. When the pack is uncomfortable, it will not charge at its maximum rate. This isn't really a problem for at-home Level 2 or L1 charging, where the slower maximum speeds won't be as significantly impacted. But, for fast charging, like you might do at a public charging station, overly cold temperatures could more than double charging time. 

So, as the ASPCA says, if you're cold, they're cold, but taking your batteries inside is a little more complicated than letting your pooch crash on the kitchen floor. 

That makes it all the more important to buy a car that can manage the temperature of its own battery packs. Thankfully, technology has come a long way in that department.

In the early days of mass-market electric vehicles, such as cars like the first-generation Nissan Leaf, there wasn't as much understanding of the need to keep EV batteries in their optimal temperature ranges. Those early EVs lacked what's called active thermal management, which is a system that can regulate the temperature of the cells within an EV's battery pack.

Today, most EVs from major manufacturers have some sort of active thermal management system. These may be as simple as fans blowing over heat exchangers to keep them from getting too hot or more advanced systems that use liquid cooling to manage the temperature. In addition to these methods, there is also research ongoing  into advanced phase-change materials that can passively store and release heat.

Most of an EV's thermal management actually focuses on keeping its battery pack cool. Excessive temperature is a far greater risk than cold temperatures. Battery packs generally get pretty warm in use, especially if you're driving at a high speed or on a hot day. If a battery pack gets too hot, it has the potential to combust, which nobody wants. 

But when we're talking about charging an EV in cold weather, the goal is to warm the battery pack up to its optimal temperature range. The act of charging a battery will cause it to warm up on its own, but since an overly cold battery cannot reach its maximum charging rate, it may never reach that optimal temperature on its own. It needs help.

This is where battery preconditioning comes in. Battery preconditioning simply involves heating the battery to an optimal temperature range to ensure that it's ready to accept its maximum charging rate as soon as you plug it in.

Different EVs rely on various internal techniques to increase the temperature of the pack. Many simply rely on heat elsewhere within the car's systems, like the motors or other components, to raise the pack's temperature. Other cars have internal heating systems to raise the overall system temperature. Regardless of how it's done, the result is a battery temperature that's up to the optimal level for immediate charging.

And virtually all modern EVs can do this, so the good news is you don't have to worry about cross-shopping. Almost all of them do it automatically, so you don't even have to do anything to enable it. Battery preconditioning is typically auto-enabled whenever you use the car's internal navigation and choose an EV charger at a destination.

Finally, make sure you pack some warm gloves and a hat. Even if everything goes beautifully and the charging session starts and stops automatically, you'll probably spend a few moments longer than you'd like uncoiling and re-coiling the charging cable and dancing back and forth while waiting for the charge to start.

If you can, keeping a spare set of gloves in the car is a good idea, if only so that your glovebox can live up to its name. Otherwise, we'll have to start calling them napkin boxes.