Why does my electric car’s range drop when the weather is cold?

Electric car (EV) adoption is picking up pace as we head towards 2030. That's the deadline the government has set itself to make sure all drivers are doing their bit to improve air quality and minimise climate change. But anxiety around the range EVs are capable of hasn't abated yet, despite car makers improving the range of newer models with bigger batteries and better technology. That's because car batteries are affected by the cold and with the wonderful British weather, that's something we're pretty familiar with.

As the Great Electric Switchover continues to power on into the 2020s, we reckon the nation’s science teachers are feeling vindicated. Their life’s work; finally being realised in the form of electric vehicles. When it comes to understanding how temperatures affect electric vehicle batteries, it turns out the chemistry really plays a key role.

Aren’t car batteries for electric vehicles just like other batteries?

Yes and no. Battery-operated devices aren’t anything new, of course, but due to the nature of mobility and the need to get from A to B, batteries in cars flag a whole raft of concerns we don’t have with, say, our TV remote controls. 

That said, the 12V car batteries which provide the power to ignite the spark in internal combustion engines (ICE) have always been susceptible to problems in frosty climes.

Exactly. So how are car batteries in EVs different?

In terms of being temperature-sensitive, they’re not so very different. That comes down to the way the electrons move. Remember that age-old lesson, ‘energy cannot be created nor destroyed’.

At a molecular level, we’re dealing with elements reacting with one another, transferring chemical energy into kinetic energy, exciting the electrons and forcing them to party. 

Ok, you’ve lost me. What?

Ok, at higher temperatures, atoms move more quickly, you know this from the bubbles when your kettle boils, and from the way you don’t feel like a morning run in the depth of winter on a frigid morning. Once you’ve warmed up, however, you’re more willing to jog (…ok, well, maybe not you). 

Anyway, the colder temperatures slow down the reactions in batteries, just like a chilly start slows the average human. 

Right, so that affects range because?

Well, if the air temperature is colder, the reactions just aren’t as effective. They take longer to warm up, the electrons don’t move as much, and so don’t generate as much power. What’s more, you probably have the heater on, so you don’t lose your toes to frostbite. That uses the energy in the battery too. 

All of this can result in as much as 20 per cent less range, although some car makers have mitigated that figure to as low as 10 per cent. If your vehicle has a claimed range of 300 miles, you can assume the real-world range is closer to 275 — that's at any temperature. Then you lose between 28-56 miles of range in the cold.

Wow. That’s quite a lot.

It is. And it’s exacerbated by the fact charging is also slower for the same reasons. 

A huge part of electrification is thermal management — trying to find and then maintain that sweet spot where the chemical reactions are happening most effectively for the longest time. In the same way, when you’re cold, it takes you a while to get going, if you keep jogging – getting incrementally faster – you’d eventually start overheating and that would cause you to slow down.

Same happens with car batteries, so car makers are working to air cool the batteries, while also making them warm enough to operate. That’s why more and more electric vehicles have ‘pre-conditioning’ features.

What is pre-conditioning for electric vehicles?

There are two kinds of pre-conditioning involved with EVs. The first refers to the cabin, making the cabin warm before you set off, so you can use mains power to heat the inside, rather than the battery power.

The other kind of pre-conditioning is that which protects the battery from degradation and tries to mitigate against some of the losses when charging in cold weather. It's essentially a warm-up for the battery state to make the charge as safe and as effective as possible. Again, car makers will always encourage you to pre-condition the battery on the mains, otherwise the car has to use some of the battery's energy to pre-condition itself, which eats into range.

What else should I know about driving EVs in cold weather?

You can't forget your gloves or hat, and heating the steering wheel and seat(s) uses less energy than whacking the air-con on.