Anybody who’s owned a smartphone knows they wear out after a few years. Even if you don’t crack the screen or drop it in the loo, the phone’s battery will eventually lose all its capacity, leaving you with a phone that needs charging every five minutes. Electric cars, which have batteries much bigger than the one in your iPhone, are a little bit like that, except they take decades to deteriorate and are normally guaranteed for eight or more years. Even so, there are some steps you can take to prolong the life of your EV’s battery.
It’s all in the charging
You probably charge your phone overnight or once the battery is pretty much flat. And you probably leave it plugged in until the battery is at ‘100%’, but it’s not the best way to treat your device. Charging from empty to full puts a lot of strain on your battery, and car manufacturers have worked hard to protect their cars from this kind of thing.
When you charge an electric car, while the readout on the dashboard might say the battery is at 100%, it probably won’t be. Teslas, for example, say their battery is full when in fact they’ve only charged to 95% of its capacity.
When you charge your electric car, you can often set it to only ‘fill’ up to 80%. And if you do want to charge the battery until it says it’s full, it’s best for the long-term health of your battery if you leave as little time as possible between finishing charging and using the car.
Does rapid charging degrade batteries?
Rapid chargers - like you find at service stations and some shops - might be the quickest way to refuel your electric car, but they’re also the quickest way to wear out its battery. Pumping large amounts of charge into the car over a short space of time generates heat, and high temperatures causes the batteries to degrade.
But speedy charging is handy for time-poor drivers, so car manufacturers have designed their cars to protect themselves from fast-charge damage. If it feels itself getting too hot, the car can slow down the charging until its temperature drops. Some cars can even air-condition their batteries on hot days.
Ryan Maughan from AVID Technology, a UK firm developing electric power technology for vehicles, explains.
“If the option is there to slow charge (3kW to 7kW) overnight when the ambient temperature is lower, this should be done in preference to fast charging during the day.”
Research conducted by the US Department of Energy’s Idaho National Laboratory backs this up. It tested two pairs of identical Nissan Leafs. One pair was charged using slow chargers at home, another using public fast chargers. After 50,000 miles, the difference in capacity between the home-charged cars and the rapid-charged cars was 4%.
Don’t run your car until it’s flat
Completely exhausting any battery isn’t brilliant for its long-term health. Manufacturers make it difficult for drivers to run their EVs completely flat by designing cars to shut down at, say, 2% rather than empty. So when your car complains that its battery is drained, it will still have a little bit of charge left in it - you just won’t be allowed to use it.
Don’t leave the car fully charged
If you’re planning to leave your electric car without driving it, experts say it’s best not to charge it fully first. Valentin Muenzel, co-founder of energy storage company Relectrify says: “When not in use, batteries degrade most when fully charged. So, if left for several days or weeks without use, they should ideally be kept at a relatively low charging state.
“And if you are only charging and discharging batteries a bit at a time (ie. doing a very low mileage), it is much better to do this with charge between 45-55% than between 90-100%.”
So if your electric car is just a local runabout, try not to keep it fully charged. Leaving it with ‘half a tank’ of electricity will be better for it long-term.
How long does an electric car battery last?
Car makers believe an electric car battery is serviceable as long as its capacity is at 80% or more. Putting their money where their mouth is, most manufacturers guarantee their cars’ batteries for at least eight years or 100,000 miles - not dissimilar to the point at which a regular car begins to show its age.
But don’t think that once an electric car’s battery warranty is exhausted it’ll be useless. Managing director of Renault-Nissan Energy Services, Francisco Carranza, revealed that Nissan monitors the battery life on the 400,000-plus Leafs it’s sold since 2011. He claims this reveals the average Leaf lifespan will be around 10 years. However, the batteries in those cars will be serviceable for a further 10 to 12 years.
Electric car manufacturer Tesla reckons its batteries lose about 5% of their capacity for every 50,000 miles they get driven. So if you drive 12,000 miles a year, it’ll be 17 years before your Tesla battery is down to 80%.
Which is good news indeed for people buying a used electric car. At one, three, or five years old, your new EV is only at the very beginning of its journey.