Electric vehicle batteries can last almost 40% longer in the real world than in lab tests

When we see “tested under laboratory conditions”, we often assume real-world conditions will lead to faster degradation of a product.

But experts from Stanford University have found the opposite is true for electric vehicle (EV) batteries. Their new research shows traditional laboratory testing leads to faster degradation, while real-world use gives substantially more battery life, extending the lifespan of the entire EV. Researchers found the stop-start way we drive and the variable rate the battery discharges power actually prolongs battery life by up to 38% compared to traditional tests.

This is good news for EV drivers – and for efforts to electrify transport. This extra battery life would translate to more than 300,000 more kilometres an EV could drive before needing battery replacement, the researchers say.

Longer-lasting batteries would reduce the total cost of EV ownership – and benefit the environment by getting more use out of each battery.

How do we usually test battery degradation?

Common battery chemistries such as lithium-ion will degrade over time. As lithium ions shuttle back and forth across the electrode, some will be diverted or trapped. As batteries age, they don’t hold as much charge.

So how do you measure this?

When you make an EV battery, you don’t want to spend 20 years testing its longevity before release. To test batteries more quickly, researchers have tended to estimate battery degradation rates by using a constant rate of battery discharge. Studies of EV battery degradation are normally done in a laboratory environment under controlled conditions.

In the lab, researchers subject the battery to rapidly repeated charge-discharge cycles. Power is discharged at a constant rate. Observing the gradual drop in capacity gives us the degradation levels over time. This is how we get estimates such as “retains 80% capacity in ten years time”.

But while this method is widely used, it has limitations. Discharging power at a constant rate is not how we really drive. We might accelerate fast to get onto the freeway, spend lots of time accelerating and braking in stop-start traffic, or do a quick run to several shops. Plus, much of the time the battery is not being used. Instead of a constant drain on the battery, it’s a mix.

What the Stanford researchers have done is test EV batteries in realistic ways, imitating the way we actually drive. This is known as “dynamic cycle testing”.

Mimicking real world use

To replicate real-world usage and driving patterns, the Stanford team designed different discharge patterns for EV batteries, some based on real driving data. The researchers then tested 92 commercial lithium-ion batteries for more than two years across the different profiles.

The results showed batteries tested using real life scenarios degraded substantially slower than expected and had higher battery expectancy than those tested under lab conditions. Even better, the more realistic the battery use, the slower the battery degraded.

Battery researchers have long assumed rapid acceleration is bad for battery life. But this isn’t the case. Short acceleration and regenerative braking – where EVs charge their batteries during braking – were actually associated with slower battery degradation rates.

Is this backed up in practice?

A number of other recent studies have looked at how batteries perform in practice using data from EVs in operation, including commercial vehicles. These studies also found correlations between real-world use and lower battery degradation rates.

A 2024 report by GEOTAB researchers used telematic remote monitoring to get data from 10,000 EVs. The study found improved battery technology is leading to slower degradation. Newer EVs lose about 1.8% of their health per year – a sharp drop compared to the 2.3% degradation rate in 2019.

Several factors influenced battery longevity other than use patterns. One of these is worth noting – frequent use of DC fast chargers by high-use vehicles is linked to faster battery degradation. The effect is more notable in hot climates. By contrast, slower “level 2” charging is better for battery longevity. Overall, the researchers found the best way to prolong battery life was to keep charge between 20% and 80%, reduce exposure to extreme temperatures and limit fast charging.