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For electric vehicles, the cost of replacing a worn-out battery can be quite significant.
When weighing this into the decision to buy one – such as a Tesla Model S – two key questions arise: how long is the battery’s lifespan, and how much will it cost to replace?
Launched in a slow roll-out June 2012, with many more cars coming after 2013, reports suggest that to date the lithium-ion battery has lost very little range as it ages even up to 50,000 miles of driving.
The sheer number of variables – such as charging habits, ambient temperatures, and driving styles – make this a complicated subject to investigate in the real world. Lab-based tests and manufacturer estimates on battery lifespan don’t always directly translate to actual results.
Still, by comparing a number of studies from around the world, it appears that Tesla batteries are doing respectably so far.
Range loss studies
One more-comprehensive study uses an owner survey to collect data. Hosted by Plug In America, the survey collects more than two dozen figures on each vehicle. Only info on the Model S is included in the report (the site has similar studies for other EVs) and more than 300 owners have logged in results.
A new 85-kilowatt-hour Model S is EPA rated at 253-265 miles range, and the 60-kwh is rated 208 miles.
Two different sets of information were used to better evaluate the battery’s performance over time. The first graph considers how old the Model S is, while the second looks at the number of miles on the car. For both, range loss is estimated by comparing the original range estimated by the EPA with the rated range reported when the Model S is in standard mode.
Each point on the graph shows what the difference between the original range and the current range is, and how old the car is. The second graph is similar, but compares the range difference with the number of miles on the odometer. The survey asks that drivers use the “standard mode” setting on the charger to report the car’s current range.
Overall, the trends show that even after the equivalent usage one would expect after several years, the Model S battery maintains 80-percent of its range.
When looking at the results, it’s important to focus on trends rather than individual data points. Driving on icy roads, entering the wrong data or improperly charging the battery are a few of the causes that could place a data point far from the average curve. When compiling results, outliers that appeared to be the result of incorrectly entering information were removed.
On the top graph, cars owned a minimum of six months were included, for a total of 205 data points. The oldest Model S was a little more than two years old. When looking at mileage on the second graph, 215 data points were included. Odometers between 6,500 and 91,600 were used in the data.
This was the only study with raw data available, but David Noland with Green Car Reports mentions a survey from the Netherlands with similar results.
“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,” said Noland.
“That means that after 100,000 miles, the typical Model S is projected to retain about 92 percent of its battery capacity and range.”
Replacing EV Batteries on the Model S
Estimating the battery replacement cost for the Model S is a bit of a gray area. Tesla doesn’t publish the price of a replacement battery, and owner reports range from $12,000 to $44,000. Also unknown is how much of a credit Tesla grants for the old battery when it’s exchanged for a new one.
Under the Model S warranty, Tesla covers factory defects on the battery for eight years or 125,000 miles on the 60 kilowatt-hours (kwh) battery. The larger 85-kwh battery is covered for the eight years without a mileage cap. However, the warranty doesn’t cover range loss.
“The Battery, like all lithium-ion batteries, will experience gradual energy or power loss with time and use,” states the warranty. “Loss of Battery energy or power over time or due to or resulting from Battery usage, is NOT covered under this Battery Limited Warranty.”
In comparison, the Nissan Leaf’s 24-kwh battery costs about $5,500 after the original battery is returned. Unlike Tesla, Nissan’s battery warranty does address range loss:
“In addition to the Lithium-ion Battery Coverage for defects in materials or workmanship (96 months/100,000 miles), the Nissan LEAF Lithium-ion battery is also warranted against capacity loss below nine bars of capacity as shown on the vehicle’s battery capacity level gauge for a period of 60 months or 60,000 miles, whichever comes first.”
As the Model S fleet on the road continues to age, surveys tracking battery performance will be able to better track the impact of age and mileage on range. For now, though, it appears that the average Model S battery will continue to hold 80-percent of its capacity for the first few years.