As cold weather sweeps across the U.S., some electric vehicle owners are learning a bitter truth: Low temperatures can stop the cars dead in their icy tracks.

The issue crystallized this week when some Tesla owners in Chicago discovered their EVs’ batteries had died in sub-zero temperatures. Drivers also said some of Tesla charging stations weren’t working, or if they did work that the stations were taking longer than usual to charge up their vehicles. 

“I’ve been here for over five hours at this point, and I still have not gotten to charge my car,” Tesla driver Brandon Welbourne told CBS Chicago. “A charge that should take 45 minutes is taking two hours.”

Electric vehicles, or EVs, are known for losing efficiency in cold weather, an issue that Consumer Reports investigated last year due to concerns about significant variations in how different electric cars held up in cold weather. At the same time, the federal government is dangling a $7,500 federal tax credit, a financial carrot that helped boost EV sales to a record 1.2 million vehicles last year.

“EVs definitely lose some of their driving range in extreme cold,” Scott Case, co-founder and CEO of Recurrent, a battery research firm, told CBS MoneyWatch. 

The issue is similar to what can occur with other battery-operated devices in the cold. 

“If you go skiing with your iPhone, you might notice that the battery will burn through more quickly, so halfway through the day it might run out of juice, where normally it would last all day,” Case noted.

Here’s what to know. 

What happens to electric vehicles in cold weather?

Electric vehicles are less efficient in cold weather, with Recurrent’s research finding that below-freezing temperatures reduced driving range up to 70% on 18 popular EV models.

An EV with a 200 to 215 mile range may only go 150 to 175 miles in the cold, Recurrent’s Case said, while noting even that reduced mileage is often sufficient for most drivers. “The average person with an EV drives 30 miles a day,” he said.

Still, a shorter range in cold weather could be an issue for some owners if their EV runs out of juice miles earlier than expected, potentially leaving to hunt for an available charger or, worse, stranded in dangerously frigid conditions.

Why are EVs affected by cold weather? 

First, chemical and physical reactions inside an EV’s battery require more time when the mercury drops, according to Recurrent. Because the cold slows these physical processes, that cuts down the power available to the EV. 

Second, unlike with cars powered by an internal combustion engines, EVs can’t tap the motor’s heat to warm a vehicle’s interior.

“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 in an email.

EVs rely on a supplemental heater, which Knizek noted are often “resistive heaters — much like a space heater you might use at home.” 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. 

Why don’t electric cars charge as well in the cold?

EVs can take longer to charge when it’s cold. That’s partly because most EVs are designed to boost their battery temperatures when the thermometer drops,  Knizek said. 

“This power to do so comes from the battery itself, reducing range,” Knizek added. “This also has an impact on charging speeds. If the battery is too cold, it will charge slower and may need to heat itself up before the charging speed can increase.”

Will cold weather damage an EV’s battery?

No, according to Recurrent’s Case.

“If you are in a cold climate, you are likely to have a battery that holds up over time versus hot climates,” he said. “The thing with very cold weather is it reduces range on an individual trip, but doesn’t do anything to a battery in the long term.”

Can EV owners prevent battery issues when it’s cold?

Yes, there are several tips recommended by Case and Consumer Reports’ Knizek. Both recommend warming up your EV’s cabin while the vehicle is connected to a charger and before you intend to take it out for a drive. 

“This means the car will use energy from the grid [charger] to get warm instead of the battery itself,” Knizek said. “You can use the vehicle’s smartphone app to do this or set a departure time within the infotainment screen in the car.”

Next, also precondition the battery before using a DC fast charger — a step that is typically available by pointing your navigation system to a DC fast charger or a button that can trigger the process. 

“This uses the battery energy to heat itself up to the optimal temp, which allows better fast charging performance,” Knizek said. “It costs some range to do this, but generally the payoff is worth it.”

Lastly, lower heat in the cabin and drive more slowly. “Speed and aerodynamics have a huge impact on range, regardless of temperature,” he noted.

What does Tesla say about cold weather?

Tesla didn’t immediately return a request for comment to CBS MoneyWatch, but its website advises owners to keep the battery charge level above 20% during bitterly cold weather. 

The automaker also says it’s normal to see energy consumption increase because Teslas use more energy to heat the battery and cabin.

“We have made several updates to improve your driving experience in freezing temperatures, including better overall thermal performance, quicker Supercharging and improved cabin conditioning,” Tesla notes on its site.

Are there other issues with EVs?

Even in optimal weather, some electric vehicles fell as much as 50 miles short of their advertised driving ranges, according to Consumer Reports. 

And another study by the advocacy and product testing organization found that EVs have nearly 80% more mechanical problems and are generally less reliable than gas-powered cars. 

The Chicago-area Teslas that ran into battery problems during the cold snap this week probably won’t change anyone’s mind about buying an EV, Case noted.  

“Everybody who wasn’t going to buy one feels great with their decision because they saw the pictures out of Chicago, and everyone who was going to buy an EV has already decided,” he said.