Electric car battery life: how to preserve your battery
As well as purchase price and driving range on a full charge, battery life is one of the top concerns for buyers of electric cars. And rightly so, as most use lithium-ion batteries – the same technology as your phone or laptop. And as we've all experienced, they lose some of their usable capacity over the course of their life.
But while the basic science of your phone battery and an electric car's battery is the same, there are large differences in how they're charged and discharged. Unlike your phone, most car batteries have a built-in buffer, which means you can never really drain them to a true 0% or charge them to a true 100%. That’s because it’s the continual 0-100% charging cycle that's most damaging to batteries over a relatively short timespan.
That’s fine in a phone, as most people replace their handsets every two or three years. Fortunately, most carmakers provide a standard eight-year or 100,000-mile battery warranty and will cover a certain amount of battery degradation during this time. So new and used electric-car buyers can feel confident.
For peace of mind, check out the 350,000-mile Tesla on YouTube. It’s still on its original battery and has only suffered 13% degradation. First-generation electric cars like the Nissan Leaf have been around for over 10 years now and, according to our sister website Auto Express’ Driver Power owner satisfaction survey, that's the 10th most reliable used car in the UK; more than 90% of owners have experienced no problems at all with their cars.
However, there are steps you can take to make sure your electric-car battery stays in good health and prolong its lifespan even further.
How to prolong your electric car battery’s life
1. Don’t overcharge it: keeping your electric car fully charged can actually damage it. That said, most electric cars stop charging when they reach capacity.
2. While electric-car batteries have a built-in thermal management system to keep them cool, it’s still worth seeking out a shady spot on a hot day, or even a garage or car port if you plan to charge at home.
3. A battery expert on a Tesla forum (with a PhD in electromechanical engineering) recommends keeping your state of charge between 15% and 90%, others 25%-75%, but advice varies. Some say 20%-80%, but fundamentally, the rule is don’t overcharge it or let it go completely flat.
4. It’s also advisable to avoid immediately charging your electric car following a particularly spirited drive. Give the batteries a chance to cool down first.
5. Limit your use of fast chargers. Obviously, there are times when you need a top-up in a hurry, and the fact they can give you a quick boost of up to 80% in a short space of time will be invaluable to higher-mileage drivers. But don’t rely solely on fast chargers to keep your car topped up, as they’re not good for the batteries in the long run. Slow charge whenever you can and especially if it's cold outside.
6. Don't park your car uncovered for long periods of time in very hot conditions.
How much does a replacement electric car battery cost?
A new battery for the world's best-selling electric car, the Nissan Leaf, costs in the region of £5,000, but the price varies considerably among manufacturers. You can also buy a refurbished one for about half the price.
However, unless the car has been particularly badly treated, you shouldn’t need one for many years to come. If your car is less than eight years old, a particularly degraded battery should be covered under warranty, regardless.
Should I be worried about battery degradation?
Using data from GPS fleet tracking firm Geotab, Select Car Leasing analysed 64 electric cars built between 2012 and 2019 to see how battery degradation affects electric cars, and whether or not newer models are more resistant to the effect.
The Nissan Leaf was picked as a particular example, as it was one of the first modern mass-produced electric cars to be sold in the UK. Select Car Leasing's study found those built between 2013 and 2013 will today have around 80% of their battery capacity left.
Earlier modern electric cars are particularly prone to battery degradation, the study claims: a 2013 Leaf lost 3% of its capacity after one year, a 2015 model lost 6% the first year, while a newer, more advanced 2019 model lost just 1%.
According to the study, the electric (and plug-in hybrid) cars with the lowest percentage of battery degradation included the Audi A3 e-tron (0.3% year-one degradation), Tesla Model 3 (0.6%) and Tesla Model X (0.7%), along with other favourites like the BMW i3 (0.9%) and Tesla Model S (1.1%).
In contrast, at the opposite end of the study's results, some popular models returned some less impressive battery degradation results. The Mitsubishi Outlander PHEV was the worst hit, with 4.1% of its battery capacity lost in the first year. The Kia Niro PHEV lost 3.5%, the Volkswagen e-Golf 1.7% and the Kia Soul EV 1.6%. The popular Volkswagen Golf GTE didn't fare too well, either, with 1.7% of its battery capacity lost in the first year.
Overall, the study shows that newer electric cars tend to be less prone to battery degradation – so it pays to choose as new an electric car as you can afford when buying used.
What should I do if I’m buying a used electric car?
The most important thing is to check how much of the manufacturer’s original battery warranty is left. It's worth getting the car’s battery status checked at an independent specialist, too. The good news is that in some cases it’s possible to change the individual cells rather than the whole pack, which is substantially cheaper.