A new study from Recurrent shows that the average Range Score for Teslas owned and operated in cold and marine climate zones are higher than those for Teslas owned and operated in hot climate zones. These were average results, and the Range Score of an individual vehicle depends on how the car is cared for. Dealers who provide tools such as Recurrent’s Verified Reports give EV shoppers the information they need about how a battery is holding up. 

This map shows the distribution of range scores for 2020 Tesla Model Ys so that we could control for the age of vehicles. 

What is a Range Score? A car’s Range Score is a value that captures how much of the vehicle’s original range is still expected today. For example, a Range Score of 90 means that we expect the vehicle to get 90% of its original range. Note that Recurrent uses observed range when new, rather than EPA range, which can often be inaccurate from day one. 

What are Climate Zones? Climate zones are designated by the US Department of Energy and are split into “humid hot,” “dry hot,” “cold,” “very cold,” and “subarctic.” We grouped together the two hot climates and three cold climates plus the “marine” zone, for this study. The “mixed” climate zones saw Range Scores in between the other two groupings. This finding holds true across all models and model years, but is most pronounced for the Model Y. 

Why Teslas? We did this research on Teslas for two reasons:

  1. They are the most numerous EV on the road and in our community, so we have the most data, and,
  2. They are very proactive about battery thermal management. Tesla’s systems will cool or heat the battery to a safe and healthy temperature regardless of whether the vehicle is plugged in. In terms of battery cooling, Tesla has a passive and an active system. The passive cooling system works all the time, while the active thermal management is rumored to turn on at 45 degrees C (or 113 F). The takeaway: Tesla offers great protection against the environmental effects on battery health. 

What causes battery degradation in the heat?

Batteries are a lot like people - always aging. We can do things to reduce these effects, like exercise and sleep, or things that accelerate them, such as smoking and tanning. 

The same is true of batteries, and being exposed to heat is a lot like smoking cigarettes. Environmental heat contributes extra energy to the electrochemical reactions in the battery, which can accelerate unwanted chemical reactions that age the battery prematurely. The generally accepted threshold for accelerated battery degradation is around 30 degrees C, or around 86 degrees F. 

You can read a lot more about the science behind heat and battery degradation here or the short-term effects of heat here. 

What can you do to protect your car’s battery?

Some of the EVs in our study may have lived in hot climates, but still have healthy batteries and great Range Scores. The chart below compares the distribution of Range Scores for the “hot climate” and "cold climate" Model Ys. How is it possible that some cars fare just fine in the heat?

Range Scores for Model Ys in hot and cold climates

Just like how good sleep and exercise help protect people from aging prematurely, there are steps owners and drivers can take to protect their EV batteries from the heat. A few of these are simple, and a few others may take some consideration or planning. 

  1. Try to park in a garage or in the shade when it's very hot and sunny. It really will make a difference, especially if your garage is climate controlled, or even a little cooler thanks to in-home AC. 
  2. If you have to leave your car in the heat or sun, better to leave it halfway charged, as opposed to fully charged. This is because the battery is more stable at half-charge, meaning there are fewer side reactions going on. 
  3. If you're interested in an EV and know it will be exposed to high heat with little shade, consider a newer LFP battery, which tends to be more resilient in high temperatures. 
  4. At the very least, if you live in a hot climate, ensure that your car has an active thermal management system, and try to leave it plugged in - with a charge limit set - when not in use. For many cars, battery cooling will start at a lower temperature when the car is plugged in than when unplugged.   

Are there risks in the cold weather?

While cold weather can cause temporary performance issues in electric cars, it does not cause permanent damage. Cold-weather range loss is due to the energy demands of heating the cabin and the battery - the energy to warm things up comes from the same place as the energy to power the car. But, since cold weather does not have the same electrochemical effect as heat, this range loss is short term and the car’s performance will return to normal when the weather warms. Think of it this way: when you have a cold, you may not be able to run a mile very fast. But the change is only temporary.  

Takeaways for shoppers and drivers  

If you’re shopping for - or caring for - an EV, a hot climate is not necessarily bad news. It’s important to know how a car was stored, charged, and used. If you own an EV and are connected to Recurrent, we already factor in your climate zone location history to your Range Score. If you’re shopping for an EV, Verified Recurrent Reports also incorporate this data. You can ask your dealer to verify their vehicle reports with us to find out how a car’s location history may have impacted it.