Question of the week: Why is my hybrid less economical in cold weather?

David Ross, Editor
Fri, 13 Dec 2024

Dear Honest John,

"My Kia Sportage MHEV seems to be doing around 15% less miles per gallon since the weather turned colder, with the battery power cutting less regularly despite saying it's well charged. Is this a fault with my car or something all electric vehicles suffer with which has not been publicised?"

- EP

Dear EP,

Electric cars perform less well in cold weather due to the effect of temperature on battery efficiency, as well as increased demand for energy from the car itself for things like cabin heating. This is something we have reported on previously, such as in our long-term tests of EVs like our Audi e-tron GT.

However, mild hybrids have small batteries compared to EVs and are commonly fitted with nickel metal hydride batteries which are less affected by cold weather compared to lithium ion batteries in EVs. Also the mild hybrid system contributes a small percentage to how the vehicle operates compared to an EV which is solely reliant on the battery.

More crucially, EVs, hybrids, petrol and diesel cars all perform less well in cold weather. Although colder air temperatures are potentially beneficial to the combustion process in terms of intake air density, the flip side is that petrol and diesel engines take longer to warm up in cold weather.

That means the fuel mixture is likely to be richer for a longer period of time, the oil remains below optimum temperature for longer which means more internal friction. Even things like denser air which increases aerodynamic drag and reduced tyre pressures can play a part.

Some of these factors will be eliminated once the vehicle is up to temperature, but it will take longer to reach this point in cold weather and on shorter journeys may not happen at all. Some hybrids and mild hybrids may not use their electrical power until the car is up to temperature, so we would expect a reduced amount of electric running or electric boost in cold weather, with a subsequent reduction in fuel economy.

Ask HJ

Does the cold weather affect electric car range?

Does extreme cold weather adversely affect EV range?

Yes - expect the real-world range of an EV to drop as much as 20% in cold conditions. That's partly because the batteries don't perform as well in cold conditions (you may have noticed your smartphone's battery doesn't last as long in extremely cold weather), but also because you'll need more power-hungry features in winter (things like the heater and headlights). There are steps you can take to extend the range when the weather's cold - for example, you can use the car's pre-conditioning feature to warm the car's cabin and defrost the windows while it's charging at home. This also has the advantage that the car's nice and toasty when you get in it in the morning!

Answered by Andrew Brady

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