Tips for extending EV range in winter

All cars lose range in winter, but for different reasons. Standard combustion (ICE) engines need to heat up before the engine works properly, but once they do they have plenty of waste heat to warm the occupants. ICE cars are sometimes hard to start, especially when it is very cold. And we all know that batteries work more poorly when they are cold. But it turns out that cold batteries are only a minor problem for EVs, and the shortage of waste heat can be a liability. I learned this from several superb posts by Recurrent Auto. Recurrent Auto is an independent battery evaluation firm that researches EV battery performance and offers their predictions about the lifetime remaining on a specific EV to buyers (free) or sellers of used EVs. If the sale is person-to-person and the seller has allowed Recurrent Auto to monitor the battery health of their car, the service is free to the seller as well.

One recent post (recurrentauto.com/research/winter-ev-range-loss) evaluated the nation’s twenty most popular EV models for their winter range loss and found that the efficiency of these models averaged 80% of that at their optimal (~70° F) operating temperature. That is, the range loss (in actual use) was about 20%, and most of the loss was due to the need for heating the occupants (not the battery!). In most cases you have greater influence over winter driving efficiency by changing your heating habits, not the car. However, there were significant differences between models (detailed near the end of this article). If you haven’t bought your next EV yet, see those recommendations for particularly efficient winter vehicles.

Given that most of the range loss is due to the need to warm the occupants, this reveals several opportunities to conserve range in the winter:

• – Precondition the car’s climate before unhooking it from the charger. Most EVs have a mechanism, often accessible from your cell phone, to preheat the cabin before leaving on a trip. If you have a regular commuting time, you can easily schedule preheating to occur at a set time before you need the car. Preheating the car’s cabin can take some time (> 30 minutes if the cabin is starting very cold) and may use up some battery if the car’s heating system draws at a faster rate than the home charger can fill it back up, but it is better than doing so when the charger is disconnected (i.e., there is no back fill while driving).
• – Use seat heaters rather than heating up the cabin’s air. If it is cold enough to require heating of the cabin’s air, consider reducing the air temperature setting and allowing the seat (and steering wheel) heaters to do the heavy lifting.
• – Consider wearing a jacket while driving, especially if it is very cold outside. Wearing a jacket ensures that you will be predressed for walking to your ultimate destination.

Some additional actions help extend range in ways that don’t warm the occupants directly:

• – Precondition the battery if you can by scheduling charging to complete just before you leave on a trip. Charging warms a battery a lot, both because many batteries are preheated before and during charging to extend the battery’s longevity and because the charging process itself warms the cells. This is true even even when charging at home. My records show that a large battery warmed by charging will hold some residual heat for as many as two days in an unheated garage, but the battery’s temperature subsides exponentially, so the thermal benefits are maximal if the battery is called into service soon after charging is completed.
• – Make sure your tires are fully inflated when they are cold. As autumn turns to winter our tires lose pressure and get softer. EV tires require higher optimal pressures than ICE cars (due to the heavy batteries) and often require more pressure than cheap gas station air pumps can provide. Check with a gauge or on your dash (if so equipped). If you ride a road bike you are familiar with the greater ease of pedaling at high tire pressures; the same principle applies to EVs. Add air as the season cools; release air as the season warms.
• – If you have a choice of departure times, and you are confronted with muddy or snowy road surfaces, travel when the road surfaces are frozen, as slush and mud have much higher rolling resistance. Obviously, icy surfaces are to be avoided for safety reasons. But deep mud on unfrozen dirt roads can demolish range in my experience.
• – Turn down regenerative braking level if that is an option for your EV. Reduced regeneration is a typical attribute of “snow mode” in cars so provided; it not only reduces wasteful charge/recharge cycles when pushing through snow, but it also reduces the chances of an inadvertent skid brought on by excessively aggressive regeneration on slippery surfaces.
• – Set your car’s maximum state-of-charge to 70-80%. Higher levels can bring the battery into a state that precludes regeneration in cold weather (the battery can’t absorb additional charge when it is full and cold). Furthermore, keeping the car plugged in while maintaining a 70-80% state-of-charge will cause the car to periodically trickle charge in the winter, warming the battery.
• – If you are on a road trip and are approaching a fast charger, pre-warm the battery prior to charging. Most navigational systems will do this automatically if you schedule the fast-charge into the driving plan. If you do not pre-warm the battery, the battery will likely slow down the charging rate and – until the battery is warmed – devote most of the energy to warming it, unnecessarily prolonging the charging time needed at the fast-charger.
• – Note that EVs with lithium-iron-phosphate batteries (a few models, which keep changing) charge more slowly in the winter, though this has no effect on battery longevity. Nor does winter charging in general; batteries return to full performance when they warm up.

What if you have a choice of model to buy?

The recurrent article in the link above describes which models are the most efficient (see also below); recurrentauto.com/research/heat-pumps also has excellent information. The basic thrust is that heat pumps improve efficiency, especially if the air temperature is moderate (above freezing). The good news is that almost all manufacturers are converting their EV lines to incorporate heat pumps. For example, older Tesla S models lacked a heat pump (77% winter efficiency), whereas new Tesla S models have them (88% winter efficiency). Rivian is making all of their models with heat pumps next year.

The alternative to heat pumps is resistance heating, which is present in all EVs to deal with very cold temperatures (when heat pumps are beyond their limits). The following graph shows Recurrent’s laboratory tests of heat pump efficacy:

Two takeaways from this graph are that: 1) range loss is especially serious at very low temperatures, and 2) heat pumps don’t help much at those especially damaging temperatures (e.g., only 2% gain at 10°F). One consequence of these results is that the degree of winter range loss experienced will be highly sensitive to which part of the country you live in. Also, the benefits of having a heat pump will vary geographically.

Here are some data from the Four Corners area. Two EVs were tested over a year on a closed circuit ~ 30-mile round trip between Hesperus and Durango Colorado (116 roundtrips documented). The two vehicles were a 2021 Toyota RAV4 Prime plug-in (PHEV) with a small battery (~ 50-mile electric range), and a 2023 Rivian R1T fully electric (battery electric vehicle or BEV) with a very large battery (410 mi range). The short-range Toyota is about half the weight of the long-range Rivian and is therefore more efficient overall (it has the higher line on the graph).

Two takeaways from this graph are that: 1) there is a lot of scatter in individual trips! Factors beyond the control of the experiment (sunshine, wind speed, direction, etc.) have a major influence. Below about 45°F the clouds of points are indistinguishable by car model in this case. And: 2) the RAV4 has a much steeper response to temperature. One popular metric for comparing models in winter range-loss is the percentage range lost from 70°F to 32°F. In this case the Rivian is 90% efficient (10% loss) at 32°F whereas the RAV4 is 75% efficient (25% loss). As you will see below, these estimates diverge appreciably from the values Recurrent obtained by averaging EV performance over the entire United States.

The following table from Recurrent expresses the average winter range-loss experienced by drivers (at a wide range of temperatures) across the United States for various selected models (broken down by whether the model year did or did not have a heat pump). The most efficient models are at the top of the chart.

The takeaways from this table are that both model and heat pump matter, though most newer models will have heat pumps, (but ask before buying!) and that real world experience in the Four Corners does not closely match these percentages, which are, however, useful for comparing models. For example, the Rivian R1T was rated at 19% range loss for the US overall, but achieved 10% in Durango, Colorado. As always, test performance may not match your personal experience, as the tests depend on factors such as temperature, travel distance, time-of-day, driving behavior, and other factors that differ from your personal needs. However, with the exception of a few of the models at the bottom of the table (note the concentration there of legacy manufacturers), winter range-loss is a relatively mild concern, at least in the Four Corners. If you drive a lot in the winter, target models that have batteries large enough to absorb the 10-25% range loss that may be experienced between recharges.