A study of over 6000 EVs found that battery degradation is much slower than common perceptions

EV battery lifespan is one of the most commonly misconceived parts of electric car ownership. Perpetuated by shows like Top Gear and misinformed pub or office banter, some people will have you believe that after a few years, an EV will barely be able to get off the drive on a charge, but the truth is much more positive.

US-based telematics firm, Geotab, helps manage fleets across the 'States meaning it's privy to rather a lot of data from EVs; 6300 of them in fact. More to the point, it has been monitoring them as far back as 2012, all the while keeping tabs on how well the batteries were holding up to repeated charging and discharging cycles.

Now after all those years and hundreds, if not thousands, of charging cycles rather than barely being able to manage a slow drive round the block, somewhere around 80 per cent of original capacity remained. And even that varied, with the Chevrolet Volt (admittedly a range extender EV) only losing around five per cent of its battery capacity in over six years.

Built-in safety

One of the reasons why you might think that an EV's battery is only good for ballast after a few years is due to the way phone batteries decline. You know the drill – your fancy new smartphone starts off lasting well over a day on a charge with modest use, but before you know it you're carrying a USB cable everywhere you go.

The thing is, phone batteries are hardly the most refined lithium-ion storage systems out there. They're designed for a few hundred charging cycles of truly effective use – which is fine when you're replacing your phone every 18 months or so. An EV battery is good for over a thousand, and Tesla reckons it's developed a battery with almost no degradation after 4000 cycles. Furthermore, when a smartphone battery gets to zero per cent, it has nothing left; nada. Nothing. Zilch.

When an EV battery gets to the point that the car won't move any further, it still has capacity left. But the manufacturer has stopped you from being your car's own worst enemy by only allowing you access to around 75 per cent of its true battery capacity. This is because degradation is at its highest in the first and last stages of charging, so by building in a low and high battery buffer, the condition of the cells is maintained as well as can be. And whilst EV batteries will see an initial drop-off in performance, that rate of degradation slows very quickly thereafter.

As manufacturers get more savvy with how best to maintain batteries, their effective lifespan will continue to increase.

What should you know?

First thing's first, don't take our word for any of this. Geotab's data is available for you to play with and dissect by vehicle model (most of which are available in the UK) and the car's year of manufacture. You can check it out here.

The takeaway point here is that modern EV batteries will by and large outlast the useful life of the car they're powering. Most manufacturers are already offering warranties which guarantee that after eight years or 100,000 miles a lithium-ion car battery will have at least 75 per cent of its original capacity left. And you can bet that they're not planning on having any claims against that guarantee.

Here's five quick-fire nuggets of truth that you can commit to memory to silence the critics of EV battery life.

  • On average, EVs lose less than 2.5 per cent of their battery capacity per year.
  • Liquid-cooled batteries decline slower than air-cooled ones, with the former degrading almost half as slowly in some circumstances.
  • The bigger the battery buffer as mentioned above, the slower the decline.
  • The UK's cool climate means that we're well-placed to benefit from longer battery life as EV power packs prefer cooler temperatures.
  • Frequent DC fast charges speed up degradation, but as the input level increases, the comparative rate doesn't. More to the point, in cooler places the decline isn't as bad during DC fast charging.


400,000 mile Tesla Model X

If you're still not convinced that EV batteries can last the course, electrek over in the USA have bought a 400,000 mile Tesla Model X which must be one of the highest mileage EVs in the world.  The car itself, a 2016 Model X 90D, is actually on its second battery, but the first lasted 317,000 miles and wasn't changed due to degradation, but rather because of a more fundamental issue with the hardware which had made it unusable. Thanks to the firm's powertrain warranty, the battery was actually replaced for free.

Now almost 100,000 miles into its second battery, it has seen around 10 per cent degradation which is actually considered high. According to electrek, the 90D battery is known for worse degradation than other Tesla units which typically lose less than 10 per cent over 160,000 miles.

Tesla's battery warranty guarantees 70 per cent capacity after eight years and up to 150,000 miles depending on the model. They won't be swapping too many, given the evidence, and quite aside from the battery degradation issue, 400,000 miles is a lot for any car to cover over four years, so it goes to show that EVs aren't only good for shorter trips.

Second life

Increasingly, the industry is coming up with innovative ways of recycling, reusing or repurposing 'spent' EV batteries, giving them a second life and doubling their use. We've reported on a number of different schemes so it's worth a look here.

In terms of recycling, whilst the industry has some way to go to get properly good at it, the fact is that almost the entirety of an EV battery can be reused in some way – though often in going back into the battery production line.

The simple fact is, though, that despite the misconceptions, journalistic jingoism from some quarters and simple lack of effective communication from manufacturers, EV batteries really do have plenty of life in them. Worrying about capacity in ten years’ time needn't be a deciding factor when thinking of buying one.


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