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EV Charging Tips to Prepare for Extreme Weather

(Note: The concepts in this article apply to fully electric cars, as well as plug in hybrids, though the negative impacts are much greater for fully electric cars.)

The future of transportation is electric, and electric vehicle (EV) sales have continued to grow in the US - reaching an estimated 1.4 million vehicles sold in 2023. [1] The steady increase in electric vehicles on the roads has led to a better understanding of factors that impact charging efficiency – including the weather. Extreme temperatures and weather events can affect EV drivers by impacting charging times, battery health, and driving range. However, while extreme weather may adversely affect EV range and charging, several steps exist to mitigate these impacts.

Cold Weather Impacts

While EV chargers should operate as usual, cold temperatures may affect how long an EV takes to charge due to vehicle battery changes. There are two important factors to recognize about your battery in cold weather:

  • EV charging in cold weather and snow.

    Slower Charging Rates: Charging rates may not have a significant impact if charging from a home or a garage for an overnight charge. However, if EV drivers are mid-trip or on a tight timeline to reach their destination and, therefore, have less flexibility, slower charging rates may impact trip planning and schedules. Figure 1 shows that in the northern areas, the red color indicates large impacts on battery charging due to cold temperatures; in the green areas, which are warmer, the impacts are much lower.

 

Map showing predicted state of charge on Median-Temperature Days.
Figure 1: Predicted State of Charge on Median-Temperature Day Across the U.S.
  • Lower EV Range: In cold weather, the battery's chemical reactions slow down, making the battery's discharge cycle less efficient. As a result, the range of your EV may be affected.

Hot Weather Impacts

Additionally, charging an EV in hotter temperatures may affect charging times and the health of the EV's battery. There are three hot weather impacts on EV charging to keep in mind:

  • Black SUV charging at EV station in garage.

    Less Efficient Charging: The US EPA's ENERGY STAR Program found that during periods of extreme heat (higher than 80 degrees Fahrenheit), the efficiency of EV chargers is slightly reduced. [2]

  • Decreased Battery Performance: Increased internal resistance can cause the battery to generate heat, which can affect battery performance and limit driving range.
  • Potential Battery Degradation: While battery capacity naturally decreases over time, charging in hotter temperatures may reduce the charge a battery can hold even further.

Additional draws on the EV battery, such as battery and cabin heating and cooling systems, could also limit the range. However, it is also important to note that with the progression of EV technology, the range of electric vehicles has consistently improved, with many EVs now achieving several hundred miles of range on a full battery.

How EV Drivers Can Prepare for Extreme Weather

Extreme weather only affects EVs under specific circumstances. Still, EV drivers can mitigate the effects on their EV charging and driving experience by taking preventative measures:

  • Mom and son plugging EV charger cord into car.

    Passive Temperature Control: If possible, park in a garage where temperatures may be regulated or exposure to the elements is limited. Parking in the shade can also help minimize the impacts of hotter temperatures on EV charging times and the health of the EV battery.

  • Pre-plug Before Departing: Pre-condition the vehicle by turning on the heater or A/C while the car is plugged in and waiting several minutes prior to driving while the vehicle is still connected to the charger to maximize range. This ensures that vehicle temperatures are regulated and that the battery has sufficient charge to minimize the initial draw on the battery. If the car remains plugged in overnight, the vehicle will have enough time to reach a full charge.
  • Slow Down:  Operating your car at lower speeds will boost EV range in any weather. Slowing down on the highway will allow your car to save energy. For example, a vehicle running at 60 miles per hour (mph) uses less energy than one operating at 75 mph, so keeping your speeds lower will boost your available EV range. EV drivers can also use their vehicles' ECO mode, if available.
  • Avoid Charging to Maximum Capacity: In hot weather, charging up to 80% instead of full capacity can decrease the stress on the battery by limiting internal resistance.
EV dashboard showing charging level.

Energy-efficient chargers and evolving battery technology can provide energy savings and greater range to help alleviate extreme weather charging impacts. Note that extreme weather only impacts EVs in specific circumstances; EV chargers located in indoor garages or EVs used for short trips within their battery range might not experience any problems.

Choose an ENERGY STAR Certified EV Charger

While there are several measures that you can take to help your EV and EV charger work efficiently, the easiest and most effective way to maximize energy efficiency is by using an ENERGY STAR certified EV charger. Here are some of the benefits of choosing ENERGY STAR:

  • EV chargers that have earned the ENERGY STAR label are 40% more efficient when in standby mode (roughly 85% of the time they are plugged in), reducing energy waste and charging costs.  
  • UL and ETL certification marks.

    Several manufacturers who sell EV chargers through popular online marketplaces make false safety and performance claims for their products. All ENERGY STAR certified products are thoroughly tested for safety and energy use and are verified by nationally recognized independent certification bodies.  

  • ENERGY STAR certified EV chargers use industry network communication standards. For the consumers, this means that the chargers are designed to work with a wide variety of other devices (wi-fi routers, electric utility energy management and price signals, etc.). While these communications protocols are still developing, choosing ENERGY STAR today means that you are aligning with emerging industry standards.

Where to find ENERGY STAR Products 

The ENERGY STAR list of certified EV chargers has grown to include more than 300 unique models from over 50 manufacturers. The list is available on the ENERGY STAR Electric Vehicle Charger AC Output and DC Output Product Finder.  

The EPA ENERGY STAR's Electric Vehicle Charger webpage provides additional guidelines and resources for potential EV charger purchasers. 

 

  [1] https://www.anl.gov/esia/light-duty-electric-drive-vehicles-monthly-sales-updates

[2] https://www.energystar.gov/products/spec/electric_vehicle_supply_equipment_version_1_1_pd

Author

Peter Banwell, ENERGY STAR Certified Products