Tesla Model S in Albuquerque's 'snowstorm' during NY-to-California road trip [photo: David Noland]Enlarge Photo
One of the things electric-car owners worry about is long-term battery degradation.
It’s a well-established fact that lithium-ion batteries gradually lose capacity as they undergo numerous charge/discharge cycles.
We owners understand that our range will gradually decline over the life of the car. The critical question is how much.
My 2013 Tesla Model S, when new, had an EPA range of 265 miles. But six or eight years down the road, with 100,000-plus miles on the odometer, there’s no way to know what my range will be.
It’s an especially worrisome question for Model S owners, for two reasons:
First, the list price of a replacement 85-kWh battery pack is a whopping $44,000. (That cost would presumably be reduced by the trade-in value of the old pack, a number that has not been publicly revealed as far as I know.)
Tesla Motors - Model S lithium-ion battery packEnlarge Photo
By contrast, a Nissan Leaf replacement battery costs $5,500, after the trade-in allowance.
Second, it’s a little-noticed fact that Tesla’s eight-year “infinite-mile” battery-pack warranty doesn’t actually guarantee any particular level of capacity. It only guarantees that the battery will work properly to propel the car.
ALSO SEE: Nissan Leaf Battery Capacity Loss: Covered By Warranty, Now (Dec 2012)
So if I lose half my battery capacity and range after three years, it would be tough luck for me.
As long as the battery doesn’t short out or malfunction, Tesla has no obligation to replace it, no matter how much capacity is lost.
2015 Nissan LeafEnlarge Photo
Again, the Leaf provides a stark contrast.
In the wake of more-rapid-than-expected battery capacity losses in Leafs in hot weather, Nissan now guarantees that the Leaf battery will retain at least 70 percent capacity after five years and/or 60,000 miles.
Nissan is the only company to guarantee long-term battery capacity.
Reason for optimism
Only time will tell, of course, what the rate of battery degradation and range loss will be for electric cars currently on the road.
But for the Model S at least, there’s reason for optimism.
2011 Tesla Roadster Sport. Photo by Joe Nuxoll.Enlarge Photo
Range losses for its two-seat predecessor, the Tesla Roadster, have proven to be less than expected since it was introduced in 2008.
And a recent unofficial study by a Dutch engineering professor shows an average range loss for the Model S even less than the Roadster’s. (Not surprising; the Model S battery management system is more sophisticated than the Roadster’s.)
When Tesla first introduced the Roadster in 2008, it predicted that the battery pack would retain at least 70 percent of its capacity after five years and 50,000 miles of driving.
But in reality, the car has done much better than that.
RELATED: Battery Life In Tesla Roadster Is Likely Better Than Predicted (Jul 2013)
In 2013, Plug In America did a study of Tesla Roadster battery longevity.
Using data from 126 Roadsters driven a total 3.2 million miles, the study concluded that the typical Roadster would still have 80-85 percent battery capacity after 100,000 miles.
Tesla Model S electric-car road trip, upstate New York to southern California [photo: David Noland]Enlarge Photo
Model S data
The recent Model S numbers from The Netherlands are even more encouraging.
Based on 84 data points from the 85-kWh version of the Model S and six from 60-kWh cars, the study concludes that the Model S will retain about 94 percent of its capacity after 50,000 miles, with losses thereafter shrinking to about 1 percent per 30,000 miles.
That means that after 100,000 miles, the typical Model S is projected to retain about 92 percent of its battery capacity and range.