Studies Show EV Batteries Are Lasting Longer Than Expected

What with concerns about affordability inflamed by the recent reduction or outright elimination of government purchase incentives, the on-again/off-again threat of international trade tariffs, and the deteriorating reputation of the segment-leading Tesla brand, it's no surprise that sales of electric vehicles (EVs) in Canada are taking a big hit. 

However, for car buyers who are currently driving an EV or are still interested in purchasing a new or used zero-emissions vehicle (ZEV), a new study found that the batteries in electric cars are lasting longer than automakers originally expected, potentially making EVs a more attractive and cost-effective option for consumers.

Real-World Driving Versus Lab Tests Deliver Surprising Results

Whether we're talking about the batteries in a mild hybrid, a plug-in hybrid (PHEV), or an all-electric vehicle, there's no getting around the fact that EV batteries degrade over time. The good news is that the majority of batteries will work for the typical lifespan of the vehicle, supported by manufacturers offering warranties of at least eight years or 160,000 kilometres that far exceed the usual internal combustion engine (ICE) vehicle drivetrain warranty of five years or 100,000 km.

The automakers hedge their guarantees by testing EV batteries before they get signed off for production. Traditionally, to evaluate a battery's longevity, scientists and engineers test the cycle lives of new battery designs in laboratories using a constant rate of discharge followed by recharging. This cycle is repeated multiple times to determine the battery's projected life expectancy. While this process has been an industry standard, a new study has found that testing in a lab is not the best way to predict battery longevity, especially for people who own EVs for everyday commuting. Instead, researchers at Stanford University took EV battery testing out of the lab and onto the roads.

They subjected them to real-world driving scenarios like congested traffic, brief city trips, and longer highway trips. Then, they parked the vehicles for hours, trying to better replicate the way EV drivers use their cars in day-to-day driving. The research team tested over 90 commercial lithium-ion batteries for over two years.

The more realistically the profiles reflected typical driving behaviour, the higher the battery life expectancy climbed. Ultimately, they discovered that battery life lasted up to 40 per cent longer than expected.

The study also showed a link between brief bursts of acceleration and slower battery degradation. This was the opposite of long-held assumptions of battery research, including that of the Stanford study's team, that quick starts from stoplights are bad for EV batteries. Pressing the accelerator pedal hard does not speed up battery degradation. If anything, it slows it down.

"We've not been testing EV batteries the right way," says Simona Onori, senior author and an associate professor of energy science and engineering at the Stanford Doerr School of Sustainability, in a press release. "To our surprise, real driving with frequent acceleration, braking that charges the batteries a bit, stopping to pop into a store, and letting the batteries rest for hours at a time, helps batteries last longer than we had thought based on industry-standard lab tests."

Although the fear from EV owners that they'll need to pay between $6,500 and $20,000 to replace their batteries before the end of the life of their vehicle is statistically low, this study from Stanford challenges existing industry assumptions about EV battery life. The findings could translate to significant cost savings for EV owners who want to drive their vehicles beyond the factory warranty coverage, as they may not need to replace their batteries as frequently as previously thought. 

While the Stanford study's revelation should reassure potential EV buyers about the long-term affordability of these vehicles, one factor that doesn't affect battery longevity is extreme hot or cold weather. While short-term EV battery degradation is accelerated at temperatures above 30 degrees Celsius and below 0°C, the first effect is reduced driving range performance, not long-term battery degradation.

Second Life Applications for EV Batteries

Beyond the benefits of longer-lasting batteries to EV owners, understanding and improving battery life is also important for applications outside the auto industry. As batteries age, they can be repurposed for stationary energy storage, supporting renewable energy systems, or providing backup power for homes and commercial buildings. Even at the end of their lifecycle, EV batteries retain value due to their materials, such as lithium, nickel, and cobalt, which can be removed and reused, lowering the demand for new mining operations.

The study also implied that the improved testing of battery longevity could also apply to other energy storage applications where aging is critical, such as glass, solar cells, plastics, and biomaterials used in medical implants.

"Going forward, evaluating new battery chemistries and designs with realistic demand profiles will be really important," said Stanford energy science and engineering postdoctoral scholar Le Xu.