Drivers of electric vehicles need to dedicate some extra time to charging once the temperature drops, according to new research from the Idaho National Laboratory.

INL, one of the Department of Energy's national laboratories, recently published this finding in the journal Energy Policy. Researchers had looked into the charging times for a fleet of Nissan Leafs in New York City, analyzing how quickly the electric vehicles charged in a variety of temperatures.

Researchers concluded that cold temperatures impacted the electrochemical reactions in the battery, resulting in a longer charge time. In addition, the vehicles' onboard battery management system limited how quickly the battery could recharge to prevent damage.

Yutaka Motoaki, an electric vehicle researcher with INL's Advanced Vehicles research group, said previous laboratory experiments have shown that cold temperatures degrade the charging efficiency of small batteries. However, the recent research focused on larger, vehicle-based batteries in a real-world setting. INL also noted that electric vehicle manufacturers often provide estimates of charging times, but don't specify the conditions for which those estimates are applicable.

"There's a lot of uncertainty about what the vehicle owner's experience would be if they drive the vehicle in Maine or Michigan," said Motoaki.

The study looked at about 500 charging events involving the Nissan Leafs, which were being used as taxis. Outside temperatures during the events ranged from 15 degrees to 103 degrees.

Charging time increased significantly as temperatures dropped. While an electric vehicle battery could be charged to 80 percent in 30 minutes when the outside temperature was 77 degrees, the charge was 36 percent less at the same time when the outside temperature was at the freezing point. During the coldest temperatures, recharging took approximately three times as long as under warmer conditions.

INL said drivers who use a heated garage and those whose trips are short enough that recharging is unnecessary are unlikely to experience problems from the longer recharging time in colder temperatures. However, researchers also noted that the taxis in the study were tied up for longer periods of time during the winter, cutting into drivers' earnings.

The study said the findings also suggest that utilities and charging infrastructure in colder climates need to be aware of the longer recharging requirement. This could include the need for more charging stations in areas with chilly winters.

Previous research has concluded that extreme heat and cold can each restrict an electric vehicle's range, since batteries do not hold a charge as well and are under greater strain due to cabin heating and cooling needs. Another INL study found that Nissan Leafs driven in Chicago during the winter had 26 percent lower ranges than the same type of vehicle driven in Seattle in the fall. Plug-in hybrid Chevrolet Volts in Chicago had a 29 percent lower range in the winter when compared to spring range.

According to the New England Climate Change Review, a project of Northeastern University, a study in the Canadian province of Manitoba found that cold weather restricted electric vehicle range by about one-third. However, low temperatures weren't associated with any difficulties in starting the vehicle.

To combat the range issue associated with cold temperatures, some electric vehicle models are now equipped with technology to warm the battery, have a separate cabin heater to reduce demand on the battery, or otherwise improve efficiency. The Department of Energy says electric vehicle drivers can also improve efficiency by driving in economy mode, using vehicle accessories sparingly, or preheating the vehicle cabin while the battery is still charging.