Many potential electric vehicle owners are apprehensive about battery life—will the battery degrade significantly over time or fail altogether? This concern is not really a surprise, as EVs are still relatively new to the market and confidence hasn’t yet built around battery longevity. With the potential cost of a battery replacement exceeding £5k, understanding the real-life performance of EV batteries over time is critical.
In order to crack long-term EV battery performance, we’ve analysed years of survey data on the UK’s most popular EV, the Nissan Leaf, from Plugin America. As part of the ongoing survey, actual car owners submit various pieces of information about their Leafs, including mileage and the number of battery capacity bars on display at the time of survey. Over time as the battery loses capacity, the car displays fewer battery capacity bars.
Our study uses data submitted by Leaf owners from 2013 into the second half of 2017. While the new 2018 Leaf has a larger 40 kWh battery and has changed the way battery capacity is displayed (instead of displaying up to 12 battery capacity bars, there is now a picture of a depleting battery like on your mobile phone or laptop), using this historical data on pre-2018 models can still give us an idea of how a Nissan Leaf battery may deteriorate over time.
Losing Battery Capacity Bars
How fast will the battery lose capacity? It largely depends on the age of the car and the mileage driven, among other factors. Our analysis shows that Nissan Leaf cars that have lost one bar and are displaying 11 bars report an average age of 2.7 years and have driven around 26,000 miles. (Note, this is not the average age/mileage at the moment when the first bar is lost, but the average stats for cars reporting the state of 11 bars. Cars would have been a bit younger and been driven fewer miles when the first bar was lost.)
It is unexpected that cars with 8 bars are younger than cars with 9 bars. A closer look at the data revealed that the cars with only 8 bars had driven 50% more per year than average. Clearly, when a car is driven more, it has been subject to more charge cycles. And it is the charge cycles that cause battery capacity degradation. Therefore, cars with higher mileage will have lost more battery capacity bars, even if they are younger.
How Many Bars Lost per Year?
Our analysis shows that by the 3rd year, drivers can expect their cars to still offer 11 bars of capacity; by the 5th year, most cars have dropped to 10 bars. This is another way to look at the data, by considering battery capacity loss by age of the car. Estimating the battery capacity bars by the age of a car only works under normal driving conditions, i.e., for cars that drive around 10,000 miles per year.
Relationship between Battery Capacity Bars and Range
Apparently, the first bar represents a 15% loss in capacity, or around 20 miles of range for the 2017 30 kWh battery. Any further bars lost each represent around 6.25% of capacity. Upon losing the first bar, we estimated that a 30kWh Nissan Leaf would deliver an average range around 110 miles per full charge, down from 130 miles with the full 12 bars.
How would this battery deterioration study of pre-2018 models translate to the new 40 kWh Leaf, which doesn't display battery bars? Assuming the battery performs in a similar fashion (even if the display has changed), we can project our learnings onto the new Leaf to estimate range as the battery ages.
Estimated Real-Life Nissan Leaf Range
|Battery Capacity||Average Mileage||Est. Range: 24kWh Battery||Est. Range: 30 kWh Battery||Est. Range: 40 kWh Batttery|
|16,148||80 miles||130 miles||170 miles|
|25,987||68 miles||110 miles||144 miles|
|32,677||63 miles||102 miles||133 miles|
|49,631||58 miles||94 miles||123 miles|
|55,572||53 miles||86 miles||112 miles|
What Does Battery Depletion Mean for You?
If you use your car for short trips around town, the gradual loss in battery capacity of an older car may not affect you much at all. A full charge could last you a few days, even in a used car. It would be a bit like having a mobile phone with a battery that could last days—you wouldn’t really suffer from a 10% reduction in battery capacity.
Those with longer range driving needs, however, might have a much different experience once their car's battery shows signs of reduced capacity. Range anxiety and more frequent charge requirements could have a meaningful impact. Less so with the new Leaf, since its battery size/range has increased 33%.
Anyone considering a used EV should keep battery depletion in mind. The rapid depreciation on EVs means that used cars might seem relatively cheap, but they may be best suited to those who drive less.
We gathered data on the age, mileage and battery capacity bars of Nissan Leaf cars from Plugin America’s survey, in which car owners around the world self-report real-life car stats. The data covers cars built between 2011 and 2017, of various age and mileage. We then analysed the information which covered over a thousand entries across 564 cars, in order to understand the relationship between battery capacity bars and the age and mileage of a car.