How long do electric car batteries last?

19 March, 2024 By: Toby Hagon

The longevity of electric vehicle (EV) batteries is one perceived barrier making some people hesitant about buying an EV. So how many years can you realistically expect to get out of an EV battery?

At a cost of tens of thousands of dollars, swapping over an old electric car battery pack for a new one is an outlay few want to contemplate when they’re already paying a premium to get behind the wheel of an electric vehicle.

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But how realistic is the requirement to replace batteries in an EV? And how will your electric car’s battery wear out over time?

It won’t last a lifetime, but you’ll get a good run out of it

Electric cars use the same basic lithium-ion batteries employed by all manner of devices, from mobile phones and laptops to power tools and smartwatches.

But the battery packs in EVs are much bigger, weighing hundreds of kilograms and sometimes more than half a tonne.

Whereas your average consumer device may be expected to last a few years, the average car is expected to go for at least a decade. In WA, the average age of a motor vehicle was 11.6 years, according to the Australian Bureau of Statistics’ motor vehicle survey in 2021.

Typically, the battery packs in EVs have a much longer lifespan than those in small devices such as smartphones, with car makers optimising the battery chemistry, materials and manufacturing techniques for a longer lifespan.

But whichever EV you buy, the battery will eventually lose its ability to store energy.

Degradation is real

Batteries degrade over time – it’s a fact of EV life. The most obvious part of that degradation is its ability to hold a charge.

Most manufacturers guarantee at least 70 per cent of the original capacity will be available after the warranty period; that’s typically about eight years and 160,000km, although some EV manufacturers are offering 10–year battery warranties.

But most manufacturers also say this is a worst-case scenario and that most batteries will have much more capacity than that once the warranty has expired.

In launching their first EVs in Australia, the all-but-identical Toyota bZ4X and Subaru Solterra claim the batteries have been designed for 90 per cent retention of capacity after 10 years (although each is warranted for only eight years at 70 per cent state of battery health).

More convincing is the research from US company Recurrent, which actively monitors battery health in 18,000 EVs. It has said it is noticing that lithium ferrous phosphate (LFP) batteries used in many cheaper (and popular) EVs are more resilient.

“They tend to be more resistant to heat degradation. It’s inherent in the chemistry – it’s a much more stable chemistry,” says Recurrent’s Liz Najman.

California has also announced new regulations that stipulate by 2030 a battery must retain at least 80 per cent of its original capacity after 10 years or 150,000 miles (241,000km). Given the size of the EV market in the western US state, it’s something likely to flow across the country and, ultimately, to EVs around the world.

Battery degradation occurs at different rates

The battery of an EV typically undergoes some energy loss early in its life. Then the degradation rate tends to reduce before a very old and high mileage battery again starts degrading quickly.

“Initially … there may be some degradation, then it kind of levels out and it very gradually declines and goes into an end state where the battery reaches an end of life and starts to decline quite quickly,” says Najman, referring to it as an S curve.

But she also confirms that in overall trends, degradation is minor, “under 2 per cent per year over the lifetime and that’s a pretty aggressive degradation”.

In other words, if you bought an EV with 500km of range, on average you could expect it to have more than 450km of range after a decade of operation.

However, collating data on older EVs is difficult because there aren’t many on the road and with their older technology, they’re often not a reliable indication of how more modern EVs will fare as they age.

“We have seen higher degradation and higher replacements in older vehicles,” says Najman.

Computer Control

EV battery life being able to outdo other consumer items comes down to computer control as part of the on-board battery management system, or BMS.

Whereas most consumer items have extremely basic battery controls, cars have advanced systems managing the voltage and temperature of each cell.

In many instances the battery temperature is adjusted when the car is parked. When charging, the car will engage charge equalisation to keep each cell in check, potentially feeding more electricity to individual cells to ensure they’re at the same levels and none is overcharged or mistreated.

It’s all about reducing stress on components and ensuring temperatures are optimised, something that is key with lithium-ion batteries.

Kate Cavanagh is the transport electrification team leader at CSIRO Energy and says the BMS is a crucial component of the charging equation.

“It has a recommended operating temperature range and it will have upper and lower threshold limits of where it likes the temperature to be,” she says. “If the battery exceeds this higher temperature [in charging state], the BMS will shut down the battery and not accept further charge.”

Heat is the enemy

A cold battery will supply electrons slower, reducing its ability to power the car. But a hot battery can result in damage to the chemistry in the battery pack. That’s one reason thermal management is such a focus with EVs.

And by hot, we’re not talking about a 40-degree day.

In the same way your phone or laptop gets warm when you charge it, a battery pack will heat up when charging.

The faster you charge it – and the more current you run through its electrical components – the more heat can build up.

Pump in hundreds of kilowatts of electricity – up to 150 times more than your home powerpoint can supply – and the temperature can quickly ramp up. The car monitors this and actively cools the battery with fans cooling a radiator filled with liquid.

Porsche is one brand working on direct oil cooling of battery cells – rather than water-based cooling through nearby pipes – something that can keep the battery at a constant 45 degrees.

Showcased in the GT4 e-Performance prototype, it’s all about maximising performance and extending the life of the battery.

The man in charge of the race car project, Björn Förster, says temperature management is a crucial part of the vehicle development, something that will ultimately flow through to Porsche road cars.

“The engineers are getting nervous when the system temperature is getting to 60 degrees,” he explains, suggesting those lower temperatures not only assist in maximising the life of the battery but also in the everyday performance of the battery.

Where you park could affect battery life

Recurrent says that where a car is parked can have an impact on its battery degradation.

“If you’re in a hot climate and the car is stored on top of black top in the sun all day every day, heat really does age batteries,” says Najman.

She says parking a car in a garage can keep temperatures down and reduce long-term battery degradation.

Charging affects degradation

Consistent fast charging can take its toll on battery health too, explains the CSIRO’s Kate Cavanagh.

“Fast charging – even though it’s quicker – it’s a higher current that’s going into the battery, which heats it up,” she says. “The hotter the battery, the faster it’ll degrade the chemistry.”

Najman adds that in moving electrons “there are micro fractures and stress in the battery material”.

“When everything is moved more forcefully you often get slightly more stress and slightly larger cracks. Higher current, or more heat, it can be a faster reaction.”

That’s why car makers recommend slower charging for most applications, something Cavanagh reinforces will work fine for most EV drivers.

Norwegian-based YouTuber Bjørn Nyland conducted battery health tests on hundreds of EVs and in 2023 evaluated a 2021 Tesla that had 94 per cent of its charging done on fast chargers.

He found that after 98,000km that car had lost 15.7 per cent of its battery capacity.

Many other Teslas he’s tested – some with much higher mileage – that had been more gradually charged, returned less than 10 per cent degradation.

Don’t go to zero

You also don’t want to take your battery down to zero because of potential damage.

Tesla says fully discharging a battery “may result in damage to vehicle components”, one reason the company has a low power consumption model at lower states of charge to minimise energy use.

The brand is not alone, with many EVs working hard to reduce the chances of a completely flat battery by warning the driver and reducing energy use (it could be by temporarily reducing the top speed or the effectiveness of the air conditioning).

There can be different performance between makes and models

EVs are still in the early phases of their development and car makers are still trying different approaches to optimising battery life.

“The real proliferation of different makes and models has been so recent that we don’t have enough history to see how they’re going,” says Najman.

However, no EVs use the full capacity of the battery, instead ignoring the very top and bottom states of charge to extend longevity.

Those with a bigger buffer – measured in gross and net battery capacity - can sometimes achieve lower degradation, says Najman.

“Some of the newer models seem to have a lot of the initial degradation already factored out by the time they’re placed in cars.”

The early Nissan Leafs have a poor reputation for battery life, largely a result of not having an active thermal management system. Whereas almost all electric vehicles have liquid systems to heat or cool the battery, the Leaf relied wholly on air cooling.

In extreme climates the battery could degrade quickly, to the point where older high mileage examples could have less than 100km of useable range.

Recurrent also nominates the 2013 Tesla Model S with a less enviable reputation and higher battery replacement rate.

But with millions of cars on the road around the world, Tesla has more than a decade of learnings, something that is improving its battery chemistry and longevity.

Still, in its 2021 impact report, Tesla stated that earlier Model S and X vehicles that were around 10 years old and had covered 200,000 miles (322,000km) experienced an average 12 per cent degradation.

Batteries are expensive – but made to last

That’s heartening, because batteries are by far the most expensive single component of an electric vehicle.

An average battery pack can cost tens of thousands of dollars, although getting prices from car companies can be challenging (in the same way as finding the cost of a replacement engine in a regular car isn’t always easy).

But fortunately, battery packs are designed to last. Just as the engine in a car is designed to last for the life of the vehicle, so too is a battery pack.

Tesla has repeatedly stated its batteries are “designed to outlast the vehicle”. Just because the warranty has expired doesn’t mean you’re up for a new battery, in the same way that an average engine will comfortably outlast its warranty period.

It just means its potential failure or degradation is no longer covered by the factory warranty (although Australian Consumer Law may cover it for longer).

Battery replacement doesn’t make sense

Just as replacing an engine on a 15 to 20-year-old car is unlikely to be financially viable, it’s also unlikely to be feasible to replace an EV battery pack unless there are major advances in tech in the future.

One option could be the reconditioning of batteries, something now common (and affordable) with hybrid vehicles.

Such industries don’t exist in Australia yet, with old or damaged EV batteries instead typically snapped up for use in EV conversions of classic cars or for static energy storage.

However, if the battery has simply lost a large chunk of its ability to hold a charge, having a short driving range could still be appealing to some – at the right price.

Charging cycles are important

Batteries are designed to be charged and discharged hundreds or thousands of times.

Each time you do that it places minor wear and tear on the cells inside the battery pack. And while there are many factors at play, battery life is to some extent related to how many charging and discharging cycles a battery undergoes.

In a basic consumer item, a battery may last a few hundred cycles, possibly longer.

While it’ll still function beyond that, it will likely hold much less energy than it did originally.

In an EV, if it were to last, say, 500 cycles then you’d have roughly 200,000-250,000km of driving.

Fortunately, most go for many more cycles. And lithium ferrous phosphate (LFP) batteries are expected to endure thousands of cycles, with some estimates closer to 10,000.

For an EV with 500km of range, that means something like five million kilometres of driving.

Clearly the rest of the car will have given up well before the battery pack.

Even if you don’t drive an EV much, though, there will still be degradation of the battery.

“Batteries age regardless of whether or not they’re used - that clock is ticking,” says Najman.

Battery health is a mystery to owners … for now

Establishing what condition a battery is in can be difficult and requires a mechanic or dealership with the appropriate diagnostic equipment.

Unlike many consumer items, including mobile phones, that make it easy to see the condition of the battery, most cars hide it within the car’s computer (the Nissan Leaf is the only one with a battery gauge in the instrument cluster which shows the batteries health). The data is there, but it’s not available to the driver or owner.

But that looks set to change, with governments already working to make battery EV health more transparent.

“California has a new law on the books saying that manufacturers will have to have that state of health measurement available to drivers and purchasers by 2026,” says Najman. “So that number will have to be part of their software systems and available and visible.”