The Art Of Charging An EV In Frigid Cold

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Some electric vehicle (EV) owners in Chicago discovered their batteries had died in sub-zero temperatures. Drivers also moaned that charging an EV at some Tesla Supercharging stations took longer than usual to complete a full charge. Other chargers weren’t working at all, so EV owners had cars towed.

The New York Times made it sound like the apocalypse had descended. Chronicling EV owners who were “experiencing a bit of buyer’s remorse,” the newspaper stated, “With Chicago temperatures sinking below zero, electric vehicle charging stations have become scenes of desperation: depleted batteries, confrontational drivers, and lines stretching out onto the street.”

Yes, EV batteries take longer to charge in single digit temperatures. Battery electric vehicle (BEV) drivers who use their heat in 20 degree weather can expect their vehicle range to drop by an average of 41%.

But automotive cold weather problems are not exclusive to EVs. All vehicle batteries, even those in internal combustion engine (ICE) powered cars, suffer in cold weather if owners don’t take the proper steps. Fluids like oil and diesel, hardware door handles and locks, and electronic components can also slow or freeze up.

There is a difference, however, between telling a story about EV battery changes during extreme cold for clickbait value or informational purposes. Autoblog notes, “There seems to us to be a fair dose of sensationalism” in the media articles coming out of Chicago. While the same slow charging phenomenon takes place with iPhones at ski slopes or other battery-powered devices in extreme cold, charging an EV in sub-zero weather has caught some EV owners off guard.

The problem can be remedied in the future, however, with prior knowledge and advanced planning.

A Primer to Charging an EV in Frigid Cold

It’s clear that relatively new EV drivers — and maybe some more veteran drivers who haven’t paid enough attention — need a primer in cold weather use of their vehicles. EV drivers need to plan ahead in order to prevent a roadside mishap due to unexpected power loss and to avoid unnecessary delays and charging costs. Indeed, savvy EV drivers already know that range is variable depending on weather, hills, speed, traffic, cargo, passengers, and interior climate settings.The Journal of Energy Storage recommends preheating batteries in EVs under cold weather conditions to improve the performance and lifetime of lithium ion batteries. Preheating can be divided into external heating and internal heating, depending on the location of the heat source.

• External heating methods are usually characterized by low system complexity, long heating time and high energy loss.
• Internal heating methods can achieve a shorter heating time, a higher heating efficiency and lower impacts on thermal-induced aging but at a higher risk in safety.

Tesla’s website acknowledges that winter changes the charging experience: “In cold weather, vehicles use more energy to heat the battery and cabin, and it’s normal to see energy consumption increase.” Tesla recommends…

• Plug in your vehicle: When your vehicle is plugged in, energy-intensive features like cabin and battery preconditioning rely on the external power source rather than the vehicle’s battery. This maximizes available energy for driving once you unplug. Leaving your vehicle plugged in whenever possible and keeping the charge level above 20% when not plugged in will reduce the impact of cold temperatures.
• Plan a Scheduled Departure: Conserve a significant amount of energy at the start of your trip by using Scheduled Departure. Once you have specified your departure time using the touchscreen or Tesla app, your vehicle prepares itself by determining the best time to start charging and preconditioning.
• Manual adjustments: You can manually pre-heat the cabin by activating preconditioning or defrost in the Tesla app.
• Engage Trip Planner: When navigating to a Supercharger, your vehicle automatically preheats your battery to maximize charging speeds once you plug in. Navigating to your destination activates Trip Planner, which routes you to Superchargers as necessary and triggers automatic preheating as you approach each Supercharger.

Tesla adds that the company has made several updates to improve your driving experience in freezing temperatures, including better overall thermal performance, quicker Supercharging, and improved cabin conditioning.

As a commenter on the New York Times piece wrote, “Use the app and Precondition: locks warm, windshield wipers operative, windshield defrosted. Excellent. Preconditioning, which even in the coldest mornings might just take 25 minutes or so, is the solution, and with the Tesla phone app you schedule the precondition ahead of time.”

Kim Burney’s Tesla Model 3 was charging just a little slower than it does in normal temperatures, she told CBS News. She had driven farther than she thought on a trip to her dentist in Ann Arbor Wednesday morning and wanted to get close to a full charge for the rest of the day’s travels. So she told the car she was going to the charging station, and it was ready by the time she arrived and plugged in.

The Research into Sub-Zero Charging Tells All

If you don’t have a Tesla, or maybe even if you do, AAA encourages BEV drivers to plan ahead by building in additional pit stops to recharge and by bundling trips. They concur that another way to reduce battery drain is by pre-heating or pre-cooling the vehicle while it is still connected to the charger. EV owners can stabilize vehicle temperatures by keeping them in a garage.

Lower heat in the cabin and drive more slowly, AAA concludes, because speed and aerodynamics have a huge impact on range, regardless of temperature. EVs lose range in the winter due to cabin heating to keep the driver and passengers warm. Unlike in a conventional car, electric cars have to use energy to produce cabin heat. In the internal combustion engine (ICE) that powers traditional cars, the “waste heat” generated by the engine can be pumped directly into the car to warm people up.

The weather doesn’t just drain the vehicle’s battery, according to AAA’s research — it also depletes a traveler’s time and money. On average, an outside temperature of 20 degrees imposes an additional cost of $24.27 for every 1000 miles. An outside temperature of 95 degrees results in an additional expense of $7.94 for every 1000 miles.

AAA tested 5 commonly available BEVs as part of its research. Each vehicle was tested at 75 degrees – the temperature established by the Society of Automotive Engineers — to obtain baseline results. Then, vehicles were tested in 20 degree and 95 degree external temperatures, with and without HVAC use. When the HVAC was not deployed, driving range under cold conditions dropped 12%, and under hot conditions, range dropped just 4%. When the heating and cooling systems were used, the battery drain was much more pronounced.

Why Does an EV React to Plunging Temps?

The problem is that, when temperatures plunge, batteries have to be warm enough for the electrons to move. And they have to be even warmer at fast-charging stations.

Inside EV batteries, lithium ions flow through a liquid electrolyte, producing electricity, as reporter Aimee Picci explains. These ions travel more slowly through the electrolyte when the temps drop, so they don’t release as much energy. The result is a drop in range and the possibility of battery depletion. The same process happens in reverse. Since electrons move more slowly, the battery can’t accept as much electricity from a charging plug. That slows down charging.

In essence, two main factors that contribute to winter range loss in an EV are chemical and mechanical, according to research from Recurrent. Most EVs are designed to boost their battery temperatures when the thermometer drops. Chemical and physical reactions in the battery occur more slowly in cold temperatures. Cold temperatures inhibit chemical reactions and act as resistance that slows down the physical processes. This reduces the EVs available power. The heaters that keep the car warm generally draw energy from the high voltage battery, reducing how much capacity is left for driving.

“From a range perspective, EVs tend to do worse in cold weather because of the need to heat the cabin for comfort,” Alex Knizek, manager of automotive testing and insights at Consumer Reports, told CBS MoneyWatch. EVs rely on a supplemental heater. Most newer EVs also have the option to come with a heat pump, which are more efficient, but they are also impacted when temperatures drop into the single digits or below.

R&D in new battery chemistries promise increased resiliency in cold weather.