The Li-Ion In Winter: What Cold Weather Does To EV Batteries

A number of you will have bought your very first EV in the past 9 or so months (i.e., when the warmer weather began in spring through to autumn). Now that we’re heading into winter, there are some things that you will need to be aware of as the colder days roll around. This is because EVs don’t behave like ICE (internal combustion engine) vehicles.

You may well be glad that you don’t have to sit there and warm up the engine before you get going (although I have to say that most modern ICE vehicles don’t need you to do this – thankfully!). However, you may find the following scenario has happened to you:

You set out on a chilly morning as usual in your PHEV or BEV and head off on your normal commute.  You had topped up the battery as usual the night before and you’ve got plenty of charge.  However, this morning, you notice that the range seems to be much lower than usual, meaning that you have to plan for an extra stop to recharge. Because you’d planned your time according to what you normally do, you don’t have time to stop off and recharge right now if you want to be in time for work, so you plan for an extra stop on the way back home, meaning that you lose out on some family time.  If you’re really unlucky, you have to limp into the charging station on the last dregs of the battery.  You may wonder what on earth happened to drain your battery so quickly – and you will have a fair amount of time to stop and think about this as you wait at the charging station.

In fact, quite a few drivers have found that in cold wintery weather, battery range can drop by as much as 40%.

Now, one of the reasons why your battery may have drained more quickly in cold winter weather is obvious. If it’s a bit chilly, your natural instinct is to turn the heater on so you don’t arrive at work with a dripping red nose and chilly fingers. Obviously, the heat that comes through the climate control system in your EV has to come from somewhere, as the system can’t use the waste heat from the engine, as is the case in ICE vehicles. This heat has to be supplied by the battery, so that puts extra demand on it, meaning that you end up with less range and a battery that drains more quickly.

Now, you could always bundle up in an extra coat, a hat, a scarf and a set of mittens for your drive to avoid using the heater and spare your battery.  However, there are other options.  The first is to make the most of functions such as heated seats.  Although these will also use the electrical energy stored in the battery, it’s a lot more efficient to heat your back and bottom with a heated seat than it is to heat the air enough to get you comfortable.  With some models of EV, such as Tesla, you can also pre-warm your car while it’s waiting on the trickle charge so that it’s nice and warm when you get in, and the electricity used to heat things up hasn’t drained the battery as much as it would have if the car wasn’t plugged in.

However, this isn’t the only reason why your battery drains so quickly in colder weather.  It’s an unfortunate reality that lithium ion batteries sulk when the temperature drops (it’s all to do with the electrochemical reactions going on inside the battery).  You may remember from back in high school science days that you can speed up a chemical reaction by adding heat and slow it down by cooling things down, and the same applies to the chemical reactions that make the battery work.  Because things inside the battery are sluggish, they don’t produce as much power, so your range goes down.  Just to add to the insult, because of this slowed chemical reaction, regenerative braking doesn’t work as well, which also adds up to an extra reduction in the range.

Now, the designers of EVs have been smart enough to know that if things get too cold, the chemical reaction will stop altogether, so they have included a heating system in the battery pack – which, of course, runs off the battery’s own power.  If you, like many others, have set your vehicle up on trickle charge overnight, you may find in the morning that you haven’t got as much charge overnight as you had hoped. This is because some of the energy has gone to heating the battery. Parking the car inside overnight while it charges can help overcome this problem, as this helps the battery stay in the Goldilocks Zone of temperature (not too hot and not too cold but just right).

Another reason why you may not have got as much charge as you had hoped is also a result of the sluggishness of lithium in the cold.  In cold temperatures, the lithium is slow to release its charge and it’s also slow to receive charge as well (charging is just a reversal of the chemical process). This may mean that you have to allow more time to charge your battery, although it’s important to bear in mind that frequently using superfast chargers will shorten your battery’s lifespan.

Some aspects of winter driving are unavoidable.  You probably will have to use the headlights more often in the darker days, along with the demisters to unfog your windows and the windscreen wipers. These will all put extra demand onto your battery.  If winter in your part of the country means strong winds, these will also put an extra demand on your battery, as getting your vehicle up to speed means that wind resistance will have to be overcome.  However, by following the advice in this article, you’ll be able to claw back a little extra range, so you see a drop of only ~10% rather than 40%.

To recap:

• Use heated seats and steering wheels rather than the climate control to stay warm.
• Preheat your vehicle while it’s still charging.
• Allow for extra charging time (and possibly more stops at the charging station).
• Park your vehicle inside overnight.
• Wear warm winter clothes inside the car so you don’t have to switch on the heater.