As frigid temperatures sweep across the U.S., some electric vehicle owners are facing an unexpected obstacle: their cars coming to a halt in the icy conditions.

This issue became apparent this week when a number of Tesla owners in Chicago discovered that their EV batteries had completely drained in sub-zero temperatures. Furthermore, drivers reported issues with Tesla charging stations, either not functioning at all or taking significantly longer than usual to charge their vehicles.

"I've been waiting here for over five hours, and I still haven't been able to charge my car," expressed frustrated Tesla driver Brandon Welbourne in an interview with CBS Chicago. "What should have been a 45-minute charge is now taking two hours."

• Tesla owners face difficulties charging batteries in freezing Chicago weather

Electric vehicles, or EVs, are known to experience reduced efficiency in cold weather. This concern prompted Consumer Reports to conduct an investigation last year, examining the varying performance of different electric cars in chilly conditions. Meanwhile, the federal government continues to offer a $7,500 federal tax credit as an incentive, which contributed to a record-breaking sales figure of 1.2 million EVs last year.

"EVs definitely lose some of their driving range in extreme cold," said a spokesperson from Recurrent, a battery research firm. 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," the spokesperson noted.

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, the spokesperson said, while noting even that reduced mileage is often sufficient for most drivers. "The average person with an EV drives 30 miles a day," they added.

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 experts. 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," a representative from Consumer Reports stated. EVs rely on a supplemental heater, which 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. "This power to do so comes from the battery itself, reducing range," the expert 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 affect the performance of an electric vehicle's battery?

No, according to experts.

"If you live in a cold climate, your electric vehicle's battery is likely to hold up better over time compared to hot climates," said an industry professional. "While very cold weather may reduce the range of the vehicle on a single trip, it does not have any long-term negative effects on the battery."

How can EV owners prevent battery issues in cold weather?

There are several tips recommended by experts. One suggestion is to warm up the EV's cabin while it is connected to a charger before driving it.

"By using energy from the grid to warm up the cabin, instead of relying on the battery, you can help preserve the battery's performance," said another expert. "This can be done through the vehicle's smartphone app or by setting a departure time within the car's infotainment screen."

Additionally, it is recommended to precondition the battery before using a DC fast charger. This can be done by inputting the destination as a DC fast charger in the navigation system or by using a designated button to initiate the process.

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.  

Electric Vehicle Sales in Chicago

A recent event in Chicago has had a significant impact on the sales of electric vehicles (EVs). According to a local resident, "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."

This statement suggests that the event in Chicago has influenced people's decisions regarding EV purchases. Those who were initially hesitant about buying an EV now feel reassured by the pictures they saw, which presumably depict a negative situation related to EVs. On the other hand, those who were already planning to buy an EV have made up their minds and are likely unaffected by the event.

The impact of this event on EV sales in Chicago remains to be seen. It is possible that the negative perception created by the pictures could deter potential buyers, leading to a decrease in sales. However, it is also possible that the event could have little to no effect on sales, as those who were already committed to purchasing an EV are unlikely to be swayed by external factors.