See all Motoring AdviceThe rise of electric vehicles hasn’t necessarily rewritten the rulebook for those buying a used car, but it has certainly enlarged it. With batteries, charging and range to think about, as well as the usual things – mileage, service history and so on – it has made things a bit more complicated. And as a result, it has also created a few fears, concerns and worries for consumers who might not be all that au fait with the new technology.
One of the concerns we hear most often is a fear of battery degradation – worries about how much battery life will remain as the car ages. After all, nobody wants to buy a car that should have plenty of range but won’t achieve the distance between charges it should. But is that a genuine concern, or is it a myth that won’t affect modern electric vehicles at all?
To answer that very question, we set about doing the research that will help you understand the ins and outs of battery life before buying a used electric car.
What’s this talk about battery life all about?
First of all, we should probably make it clear that this is the traction battery – the big battery that powers the electric motors – we’re talking about, rather than the 12-volt battery common to all cars and used to power ancillary functions. While those 12-volt batteries degrade over time, too, they shouldn’t need replacing any more or less often than the battery in a conventional petrol or diesel car.
The traction batteries in EVs, however, often use much the same lithium-ion technology as those found in laptops and mobile phones, which isn’t necessarily known for its longevity. After just two or three years, smartphone batteries can lose more than 15 per cent of their capacity, leaving users with less screen time between charges. So it stands to reason that electric cars will have the same issues, right?
That’s the logic that fuels the concerns, and there’s some truth to it. Over time and through charging cycles, lithium-ion batteries – and other varieties of battery chemistry – will degrade, leaving them with less capacity than they had when they were new. It’s especially true of batteries that have regularly been charged using the fastest charging facilities to 100 per cent. That’s because charging causes the battery to heat up, and that can degrade the battery cells.
Obviously, a car with a degraded traction battery is best avoided, because batteries are one of the most expensive single components in an electric vehicle.
How likely is it that a car’s battery will degrade?
Every battery will degrade over time, but unless the used electric car you’re looking at is especially old, we wouldn’t worry too much. Most car makers provide a battery warranty that guarantees the battery for a certain distance or length of time. For example, Peugeot offers an eight-year, 160,000km battery warranty, guaranteeing that the battery will have at least 70 per cent of its original capacity when it passes eight years old or 160,000km – whichever comes first.
In the case of the latest-generation Peugeot E-308, the warranty guarantees at least 35.5kWh of the original usable capacity of 50.8kWh will be available after eight years or 160,000km. While that might not sound that much, remember it’s a guarantee backed by the manufacturer, and most cars will likely have much more capacity available at the end of that period, especially if they’re well looked after.
How do I know if a used car’s battery is degraded?
This is the tricky part because age and mileage don’t tell the whole story. Those familiar with the car (i.e. the owner or driver) will spot a reduction in real-world range between charges as the battery’s capacity shrinks, but for those with less experience of the vehicle, it’s harder to know for sure.
There are some indicators, though. Age is a factor, as batteries will naturally lose capacity over time – perhaps losing a couple of per cent a year – and mileage is a concern, too. A car that has driven further will have been charged more often, and those charging cycles might well have depleted the battery capacity. But while those numbers may be indicators, they aren’t hard-and-fast rules. A battery that has covered 100,000km but has always been charged at home and never been taken below 20 per cent or above 80 per cent may well be in better condition than one that has always been charged at more than 100kW and always topped up to 100 per cent, but has actually only done 50,000km.
If you’re making a private purchase (i.e. you’re buying direct from the previous owner), it’s probably worth asking how the battery has been treated to get an idea of whether degradation is likely. Like smartphones, some cars will also have a function somewhere in the infotainment system that tells you the battery condition, although some vehicles will require an engineer – or at least a diagnostic tool – to tell you what’s what. Some car makers will help by providing a certificate of battery condition at each service, which tells you how much battery capacity is left.
If that kind of information is not available, take a look at other possible clues, such as the state of the interior. For example, a car that has done lots of short journeys may have creased and worn seat bolsters by the driver’s door, while a car with similar mileage and a pristine seat has probably driven further on each journey and likely used more public charging points. Again, it isn’t a foolproof indicator, but it’s an example of how a car’s condition can tell you more about its life.
How do I keep my battery from degrading?
You can’t stop batteries from degrading completely, but you can take steps to ensure they don’t degrade too quickly.
Batteries are picky in a way that fuel tanks never were, and they have a sweet spot in their operating range. They don’t like big fluctuations in temperature, and they like to be kept somewhere in the middle of their charge band.
As a rule of thumb, it’s best to keep a battery in between 20 and 80 per cent charged as much as possible, and to use slower chargers such as the 7kW domestic ‘wallbox’ charging units you can install at home. There’s nothing wrong with charging fully occasionally and even using a rapid charger (50kW or greater) now and then, especially if you’re doing a long journey, but if you keep it somewhere around half charged most of the time, it’ll reward you with greater longevity.