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Cold Weather & Winter EV Charging: Lessons Learned from Testing

Cold weather's impact on electric vehicle (EV) range is a well-known issue. Lithium-ion batteries experience reduced range in low temperatures, and this range loss may or may not be reflected in your vehicle's on-board range estimates.

It's also common knowledge that cold temperatures can lead to longer charging times. Research has explored this effect, such as studies examining the increased DC fast charging times for Nissan LEAFs in cold weather.

The slow charging process in low temperatures serves as a protective measure for the battery. When charging, an electric current moves lithium ions from the cathode to the anode in an orderly manner, similar to passengers finding their seats on an airplane. Cold temperatures slow down the chemical reactions involved in this process, causing lithium ions to accumulate outside the anode. If charging continues at a regular speed, lithium ions collide with each other, forming inert metallic compounds known as lithium plating on the anode's surface. This leads to long-term battery degradation and increased resistance, impeding the flow of ions.

EVs feature a battery management system (BMS) that controls the charging speed to prevent issues like lithium plating in extreme temperatures. The BMS monitors the battery's temperature and adjusts the charging rate accordingly. Many EV manufacturers recommend keeping your vehicle plugged in during winter to maintain battery warmth and allow for faster charging. Teslas are known to keep their batteries warm at all times, while most other vehicles only activate battery heaters when charging.

Controlled Test: Cold Weather Charging with Onboard Devices

Recurrent received a prestigious National Science Foundation grant to conduct experiments using onboard devices to verify their range data. They collected real-time data from 50 Tesla Model 3 and 50 Nissan LEAF drivers using Geotab OBD II devices, measuring factors such as state of charge, regenerative braking energy, HV battery energy usage, outside temperature, and HV battery charging energy.

Preliminary findings indicate that gross charging consumption per minute may be up to 28% higher in warm weather compared to cold weather. The exact charging efficiency breakdown for warm vs. cold weather for Tesla and LEAF vehicles is as follows:

Tesla: percent change in charging efficiency in warm vs. cold weather

Level 1: 9.5%

Level 2: 28%

Level 3: 15%

Nissan LEAF: percent change in charging efficiency in warm vs. cold weather

Level 1: -1.5%

Level 2: 23.9%

Level 3: -6%

Further analysis is required to understand these results fully and determine their implications for the broader EV community.

Uncontrolled Test: Cold Weather Charging with Citizen Scientists

Recurrent sought to test real-world charge times that drivers experience in winter. They asked participants to record data to understand how cold weather affects charging. However, this experiment served more as a lesson in experimental design.

Temperature: The average temperature for participating drivers was 10°C, with a range between -12°C and 20.5°C, which was too warm for any pronounced effect.

Vehicle Make and Model: A variety of vehicle makes and models were represented in the study, but little temperature-dependent variation in charge times was observed.

Vehicle Make and Model

We were pleasantly surprised to find a variety of vehicle makes and models in our list. A few respondents entered multiple data points for their car, which provided valuable data. However, we did not see significant temperature-dependent variations in charge times. The Nissan LEAF consistently added 22.5 - 32.2 km of range in an hour of level 2 charging, and the Tesla Model 3s on the list achieved between 56.3 and 85.3 km per hour. Note that the 56.3 km per hour added was for one vehicle; the repeat Model 3 was always between 70.8 and 85.3 km added per hour.

Here are some of the other models we saw, with the average distance added per hour:

Tesla: 56.3 - 85.3 km added per hour

Hyundai Kona EV - 37.8 km added an hour

Chevy Bolt LT - 37.6 km added an hour

Chrysler Pacifica - 34.1 km added an hour

LEAF: 22.5-32.2 km added per hour

Volt - 4.1 km added per hour (110 volt)

Takeaways: The experiment provided valuable insights into how to design better studies and gather more meaningful data from participants in the future.

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