Winter battery management key to maximizing EV range, charge times

Navistar electric truck eMV
When not in use, it's ideal to keep electric vehicles plugged in during frigid weather to keep batteries warmed up to help reduce range loss.
Navistar

While the list for winter maintenance requirements on electric trucks and vans is fairly short compared to their internal combustion counterparts, experts agree that powertrain battery management should rank at the top.

With over three million miles of commercial electric vehicle experience, which includes traversing harsh Colorado winters, Lightning eMotors CEO and co-founder Tim Reeser said the greater lesson to keep in mind is how to battle range reduction amid freezing temperatures.

Reeser said they’ve seen up to a 30% drop in range when winter comes calling since chemical reactions within the battery are slowed 

“We've got enough data on this now to feel very strong that we know the answer and that 30 percent is a good number,” he said.

According to the the Department of Energy, range can drop by as much as 41% in 20 degrees Fahrenheit. Roughly two-thirds of energy consumption was attributed to heating the cabin.

Simply put, cold weather slows down battery performance according to Ford. "Temperatures below 40°F cause the electrolyte fluid to be sluggish limiting how much power is available to discharge and how fast the vehicle can charge. When temperatures are low, you could see a reduction in range, which is normal," Ford states on a webpage aimed at improving EV range during winter.

Range can also be diminished when EVs require additional power to traverse snow-covered roads, Reeser said.  

Proper battery management can help reduce range depletion in colder temperatures which includes keeping EVs plugged in when not in use so that the vehicle’s thermal management system can keep the battery warmer.

"Whenever possible, just keep it plugged in,” Reeser said. “Because when it's plugged in, the battery management system gets to manage the thermals of the battery.”

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Voltage draw can be tailored according to fleet needs such as charging to an optimum level shortly before departure and pre-heating the cabin for driver comfort.

Ford electric E-Transit and Lightning F-150Ford recommends parking EVs in a garage to reduce the range-robbing impact of freezing weather outside.FordThermal battery management experts at Modine, which has been regulating powertrain temperatures since 1916 (Henry Ford turned to them for the Model T), say there’s a small window for optimum thermal battery management.

“A battery pack should be maintained—depending on the manufacturer—but usually 25 to 35 degrees Celsius (77 to 95 degrees Fahrenheit), so there's a narrow, ideal window for the battery pack to really maximize and minimize charging time,” said Gina Bonini, vice president and general manager of advanced thermal systems at Modine.

“The battery thermal management system is a key addition to that battery pack to maintain that ideal temperature range,” Bonini continued.

Modine’s battery thermal management system (BTMS) works to maintain an ideal battery pack temperature by circulating ethylene glycol around the battery pack. Ethylene glycol, more commonly known as coolant, can be heated or cooled depending on pack temperature.

“In cold environments, our BTMS for instance, has a heating loop,” Bonini said. “On the battery pack there'll be a battery plate or some other structure to transfer heat to and from the battery cells out into a coolant. We then heat that coolant with our battery heating loop to raise the temperature of the battery pack.”

Navistar’s director of EV field services, Kyle Maki, said battery thermal management is left up to the truck, not the drivers or fleet managers.

“Our BTMS makes it easy on the operator and fleet managers,” Maki said. “As long as the key in the ignition is turned to ‘on,’ or the vehicle is plugged into the charging station, the BTMS will operate as designed. Our engineering team did not want to force our operators to engage any switches, but to have the system manage itself.”

Once an EV is out on the road, its powertrain battery generates heat “which then needs to be removed to keep the battery pack from getting too hot,” Bonini added.

Reeser said the coolant systems in Lightning EVs are comparable to those in internal combustion engine (ICE) models.

“We run exactly the same coolant. In fact, we run the same radiator, the same heat exchanger that comes stock in many of these vehicles so it’s handled in exactly the same way,” Reeser said. “This is where fleets really like it because you don't treat it any differently than you do your ICE vehicle. You reduce it the same amount so typically it's 50% water, 50% glycol and that's what you're running.”

Training to new technology

Maintaining ideal battery range in cold weather often comes down to overall vehicle management. Ford spokesman Eddie Fernandez cited cold weather advice given to e-Transit owners.

“AAA tested the range effects of 20°F (-7°C) weather on several popular electric vehicles and found that temperature alone could reduce range by 10-12%, while the use of in-vehicle climate control could amplify range loss to 41%,” Fernandez said.

Climate control habits inside an electric vehicle, particularly during winter, play a big role in battery management, Reeser said. Some fleets may have to train drivers not to leave an electric truck or van turned on with the heater going while they’re delivering packages for example.

“You have some applications that have less risk of this idle than others, but some of this is a training opportunity and some of it's also an opportunity to talk about things that weren't historically standard in commercial vehicles,” Reeser said.

Switching off the cabin heater and turning on heated seats and a heated steering wheel while out on the road during a cold day can help preserve battery life.

“We spend a lot of time looking at heated seats in these vehicle because as you move to a heated seat, now the driver's more comfortable with turning off the heat while they're out of the vehicle,” Reeser said.

Fleets may have to adjust for longer charge times in freezing weather. Electrify America points to an Idaho National Laboratory study which found that EV batteries experienced a 36% drop in energy uptake when charging at 32 degrees Fahrenheit.

“When temperatures are low, the electric vehicle’s software reduces its charging power, and for a good reason: to help avoid stressing the battery,” Electrify America states in its tips for charging EVs in the cold. 

Drivers and fleet managers also need to be aware that regenerative braking will not perform as well in colder temperatures.

“If the battery's very cold and if it has not been preconditioned, you are limited on how much your regenerative braking will work because you're limited by how much of that energy you can absorb and put in the battery because we're going to protect the battery and limit the battery [when it’s outside of its optimum temperature range],” Reeser said.

Some similarities with ICE

In addition to sharing a similar powertrain temperature management system, some electric trucks share the same air brake system which requires the same approach to winter management such as purging moisture and checking to ensure proper air dryer performance.

“We recommend the same air brake system winter prep procedures as our diesel products,” Maki said. “Additionally, we recommend emptying the air tanks before extended periods of parked time to allow the moisture to escape the system.”

Vehicle contact with corrosive de-icers and sand is handled in a similar way.  

“Navistar encourages customers to complete the same washing procedure as they are used to, including de-icing,” Maki said. “We train our customers to not spray directly into modules and avoid close spray contact to all high-voltage cables and modules.”

The bigger focus with EV winter management, Maki said, remains on battery thermal management.

“Even though there is no concern for fuel gel issues, we will train our customers on how to properly maintain their battery packs using our battery thermal management system,” he said.