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 save money on gas, EVs can do that--but only after they've spent some time plugged into a charger.

The time it takes to give your EV a full charge depends on the speed of your charger and the maximum rate of your car, but there's another crucial factor that many people overlook: temperature.

Not only does your EV's range drop in cold weather, so does the battery charging rate, meaning more time waiting at a chilly charging station.

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

To explain why EV batteries take longer to charge in the cold, we first need a little science lesson. (If this level of detail isn't your thing, feel free to skip ahead; no hard feelings).

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 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 structure of the battery creates an electrical circuit from the anode to the cathode. The "power" comes from a chemical reaction, specifically, the flow of ions as they travel through the electrolyte, which is often a liquid-based solution. Electrons catch a ride on those ions, and it's that flow of electrons that ultimately moves your car.

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. 

So, 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 on cold mornings, 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 handle different temperature ranges, but according to recent research, the optimal range for a typical, lithium-ion battery pack is between 15 and 35 degrees Celsius, or 60 to 90 degrees Fahrenheit. 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 battery 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. Plus you're in your warm home.

But, for fast charging, like you might do at a public charging station, overly cold temperatures could more than double the charging time. 

As the ASPCA says, if you're cold, they're cold. But taking your EV batteries inside is a little more complicated than letting your pooch crash on the family room 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 the first-generation Nissan Leaf, there wasn't as much understanding around 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.

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. It's also typically auto-enabled whenever you use the car's internal navigation and choose an EV charger at a destination.

Virtually all modern EVs have these capabilities, so the good news is you don't have to worry about cross-shopping.