10 mins read
Not long ago, one of the most commonly encountered concerns about electric vehicles was the lifespan of their batteries. Naysayers would take to social media to proclaim that an EV’s battery would last a mere 3-5 years and then be landfilled – both of which are incorrect statements. Focussing on the 3-5 year claim for now, which is wrongly attributed to EVs based on the performance of batteries in consumer electronics, it’s entirely reasonable for fleet managers who hold onto their vehicles for a long time and/or clock up hundreds of thousands of kilometres in them to ask: what is the lifespan of an EV battery today? Do fleet managers risk their vehicles becoming a liability as they gradually become incapable of performing a day’s shift on a single charge, and start to fall short of making the gap between scheduled charging stops on their routes?
Some good news is offered by some of the oldest EVs on the road. While the earliest Nissan LEAFs were the exception to the rule due to their poor battery chemistry and uncooled battery pack, which led to accelerated degradation and loss of range per charge, most older EVs are still running around on their original batteries and showing little signs of degradation, such as the air-cooled battery of the Renault Zoe and the liquid-cooled battery of the BMW i3. Of course, passenger cars may not be driven as many kilometres in a year as fleets, but conveniently many of the early EV adopters were taxi drivers, which acted as an accelerated aging test for EV batteries. A prime example is the 40 kWh Renault Zoe taxi in Turkey that clocked up nearly 345,000 km and still showed a battery State of Health (SOH) of 96%. To reiterate, that’s a vehicle with a battery chemistry that is about 10 years old, and a battery design that is merely air-cooled and is therefore rudimentary and largely obsolete by modern standards, that has driven approximately double the distance covered by the average Irish car in its entire life, that has lost at most 4% of the battery’s original capacity vs when it was new. Looking at bigger vehicles, as mentioned in an earlier article, the oldest of Ember’s fleet of electric intercity buses in Scotland, which run 24/7 and are rapid charged several times a day, have each exceeded 700,000 km on their original battery packs and still have more than enough capacity to run from Dundee to Edinburgh and back on one charge.
So how do EV batteries manage to last so long while the lithium-ion batteries in mobile phones and laptops tend to last only 3–5 years? There are several key differences between the lithium-ion batteries found in EVs and consumer electronics. Firstly, EVs tend to liquid cool their battery packs, keeping them at their optimum temperature and reducing the rate of degradation, while phones and laptops expose their batteries to high temperatures that accelerate degradation. Secondly, the Battery Management System (BMS) in an EV deliberately blocks off the top and bottom few percent of the battery’s true capacity by setting conservative charge and discharge voltage limits vs the cell manufacturer’s spec sheet. This means that the EV loses a handful of km of range compared to what it could do in theory, but benefits from vastly reduced degradation compared to phone and laptop batteries that are pushed to their maximum voltages for the sake of a few minutes’ extra runtime. Furthermore, advances in cell design over the years have improved EV battery longevity by optimising the chemistry of the electrode and electrolyte, such as by introducing additives that slow down degradation reactions, and by tailoring the physical design of the cell to the demands of an automotive application, for example by reducing the amount of heat generated during fast charging/discharging, and making it easier for that heat to escape the cell before it can accelerate the cell’s degradation (which is a big factor behind the design of Tesla’s 4680 cell).
On top of this, it transpires that lithium-ion batteries actually prefer the rigours of electric vehicle driving to the constant current cycling that they encounter in the lab. A recent study by Stanford showed that lithium-ion cells that were subjected to the sort of duty cycles that would be encountered in an EV, such as stop-start driving, harsh acceleration and regenerative braking, outlived cells that underwent constant current charge/discharge cycles (which are standard procedures in the lab) by 38%. No wonder that Arval has found that the batteries in thousands of used EVs that it has sold over the past few years are outlasting expectations, maintaining an average of approximately 90% of their original capacity vs new (SOH) after 200,000 km. As for the impacts of repeated DC fast charging, another report by Recurrent found that the difference in SOH between Teslas that are routinely fast charged vs Teslas that are rarely fast charged was minimal, and lost in the margin of error.
For fleet managers looking to lease new EVs, the rate of battery degradation is arguably made a moot point by the fact that an EV’s lithium-ion traction battery typically has the most generous warranty of any component of any vehicle of any powertrain. Most EV manufacturers offer at least an 8-year, 160,000 km warranty on their EV battery packs, which means that if they reach an SOH of typically 70% or less within that time, the battery is repaired or replaced for free. Bear in mind that vehicle manufacturers are always conservative with their warranties, as they don’t want to end up paying millions of euros to replace the component in question in most of their vehicles, so this means that EV manufacturers are highly confident that their EV batteries will last comfortably beyond 8 years and 160,000 km. This shouldn’t just give peace of mind to fleet managers leasing new EVs, but to anyone buying used EVs too. Some manufacturers such as Toyota take this further by offering extended battery warranties up to 10 years or 1 million km. If you want to be absolutely sure that an EV’s battery is in good condition, a number of independent EV battery SOH diagnostics companies, such as ClearWatt, are starting to spring up that can run a test on used vehicles that you are looking to “2ND life” lease.
Some EV manufacturers are starting to become even more confident about the lifespan of their batteries. Tesla and their research partners in Jeff Dahn’s research group have been touting a million-mile battery for some time now, based on a combination of their excellent BMS, thermal management system and improved, ultra-long-life cell chemistries. CATL and bus-maker Yutong recently announced their own million-mile EV battery that has a 15-year, 1.5-million-km warranty, which in reality means that the battery is likely to be covered for the entire life of the vehicle. It’s possible that Ember’s unofficial on-road accelerated aging tests in their Yutong electric intercity buses will have played a part in giving CATL the confidence to offer such a generous warranty to its customers.
In conclusion, EV batteries are outlasting expectations, even in many of the oldest and most heavily-used EVs on the road, and each new iteration of EV battery shows further improvements in lifespan. Equally, most EV drivers will gladly give anecdotal evidence about how well their EV battery’s range has held up over time. The developments outlined above provide solid evidence that EV battery degradation is nothing to worry about, as decades of rapid progress in battery research have translated to real-world results in EVs. As such, EV battery lifespan should not be considered a barrier to the adoption of EVs in your fleet. For what it’s worth, my 10-year-old Tesla Model S has clocked up 224,000 km on its original battery, and still returns a range of 320 km per charge on the motorway. The battery’s got plenty of life left in it yet.