It's no wonder that people worry about electric car battery deterioration. Not only does a degraded battery mean a shorter range on a full charge, but buying a replacement battery, if necessary, would set you back thousands. The real question on everyone's minds is—how well does an electric car battery last?
To help answer this question for the renowned electric car maker, Tesla, we analysed owner-submitted data from Plug In America for Model S cars made between 2013 and 2019. While the technology is still relatively new to the market, we now have seven years of data from which to draw some longer-term conclusions about the longevity of Tesla batteries. This study follows our previous study of the Nissan Leaf battery performance.
Tesla Battery Degradation by Age of Car
What happens to a Tesla battery after a few years of driving and charging? As you can see in the chart below, a new car starts off giving over 100% of the EPA range, but from there the battery does indeed deteriorate over time—however by seven years old the average Tesla battery still provides around 93% of its original capacity and range.
It's interesting to see that the outlying data point in the chart shows that a car with unusually high mileage for the age (over 143,000 miles for a car less than 5 years old) has more significant battery deterioration than a typical car of the same age. This shows that mileage is also a considerable factor in how quickly a battery deteriorates—this makes sense, as more miles driven means more charge cycles, and it's mostly the charge cycles that reduce a battery's usable capacity.
Below, we've displayed the same data in a column chart so you can see the average battery capacity at each year of a car's life. As you can see, a car loses around 1% of range a year, although there is some variation from year to year. It looks like batteries loses more capacity in years 2 and 3, but this may result from noise in the data set as discussed in the discussion of limitations below.
Tesla Battery Degradation by Mileage
Will you still get decent range after your car has covered 50,000 miles, 100,000 miles or even more? The data shows that the average Tesla battery still provides over 90% of the original range up until around 150,000 miles on the odometer. Past 150,000 miles it seems that the range starts to drop off, but cars in the survey still delivered over 82% of their original range even at the highest mileage levels.
For example, the car with the highest mileage in the study was a Model S 85P that at 232,442 miles on the odometer still delivered 220 miles on a full charge (original EPA range of 265 miles), which is 83% of the car's original range.
The chart below can give you an idea of the type of range you can expect to achieve depending on how much you drive and the mileage you'd expect to put on your car while you own it.
We downloaded owner-submitted information on the Tesla Model S from Plug In America which provided data for over 500 cars including the purchase date, battery size, EPA range and, for the date of submission, the odometer reading and estimated range (for a full charge and/or a partial charge—and what percentage charge achieved at that point).
Then we had to scrub the data, looking for human error data entry mistakes. For instance, there were instances of battery charge percent that didn't make sense (e.g., 900 for the percent charged) or where it was clear that the range and percentage charge had been swapped (e.g., values 80 for range and 267 for percent charge were probably meant to be entered as 267 for range and 80 for the percent charged). We either made corrections where the error seemed obvious or deleted a data point where we were unsure.
To determine the level of deterioration in a battery, we calculated a ratio by dividing the full range at the time of survey by the EPA range for that car. This allowed us to include cars with batteries of different sizes.
For the full range estimates, we included both full charge ranges and also converted partial charge ranges, since many people do not charge their battery to 100% capacity. For these, we divided the partial charge range by the percentage charged to estimate a full charge range. For example, if an owner entered a range of 200 miles for an 80% charge, we estimated that a full charge would achieve a range of 250 miles (200 divided by 80%).
Next, we organised the data and cut it according to a car's age or mileage and graphed it. For the column charts we then grouped the data into buckets to further observe trends in the data.
This study is meant to give a general idea of how a Tesla battery performs in terms of available range over years of use and mileage. There are some limitations to this study, including:
- The percentage charge entered by owners was often rounded to the nearest 10 percentage points. This certainly creates noise in the data and estimates of range on a full charge could be off by a few percentage points for some cars as a result.
- Our calculation method to estimate a full-charge range by dividing a range at a partial charge by the percentage charged is not totally accurate, but is meant to give a ballpark figure.
- Limited number of data points for some ages or mileages makes the data less reliable and noisier.