10.07.2013 - by Tom Saxton
Battery Study Updates

At Plug In 2013 in San Diego, I presented some new and updated results from the Plug In America EV battery longevity studies.

The Original 1997-2003 Toyota RAV4 EV

First up, let’s take a look at a chart showing results from 62 original RAV4 EV owners. These vehicles started production in 1997 and leased as fleet vehicles. In the 2002 and 2003 model years, around 300 were leased or sold to consumers. The majority of those vehicles are still on the road today. They use nickel metal hydride batteries and provide over 100 miles per charge.

The horizontal axis shows the vehicle age and the vertical axis is the odometer reading. The blue dots are vehicles that are still driving on their original battery packs and the red diamonds have had their battery packs refurbished.

RAV4 EV odometer versus age by battery pack status

As you can see, these vehicles are lasting as much as 150,000 miles and 12 years on their original batteries. One intrepid owner has driven nearly 250,000 miles with a refurbished battery pack.

Tesla Roadster

In July, I released results from our Tesla Roadster battery study at Teslive. From the data collected at that point, the data suggested that the average Tesla Roadster will have between 80% and 85% of the orignal battery capacity (range) after 100,000 miles. Since then, one survey participant has crossed the 100,000 mile line within the expected range.

This graph shows the distribution of age and odometer readings among the Roadster survey participants.

Tesla Roadster odometer versus age by battery pack status

Below is a graph showing the battery capacity levels of the Roadsters still driving on their original battery packs as a percent of the original expected capacity.

Roadste capacity vs odometer

Tesla Model S

The Tesla Model S is barely a year old, so it seems pretty early to be doing a battery survey, but the owner community expressed interest so we started one up. The Model S comes with three different battery pack sizes: 40, 60, and 85 kWh. (The 40 kWh option was canceled, so only a few were sold.)

Let’s start with a graph showing the population of Model S survey participants by age and odometer, with the data points colored by battery pack size. Notice the Model S owner who has driven over 32,000 miles in less than a year!

Model S age and miles

To examine battery capacity over miles driven, the graph below shows just the 60 and 85 kWh vehicles in separate groups.

Model S capacity by odometer

So far, we’re seeing a little variation between vehicles, but basically flat performance over miles with no discernable degradation. Stay tuned for more results as we see more years and miles on these vehicles.

Driving Trends

One thing that has emerged from the battery surveys that I wasn’t originally looking for is how much owners of different models drive their cars. For each of the four survey, I’ve added up the total number of miles driven and divided by the sum of the vehicle ages to get an average number of miles driven per year of ownership.

miles per year by model

I suspect the RAV4 EV miles per year are reduced as many of those owner have picked up one of the newer EVs and shifted at least some miles away from the RAV. The same is true of the Roadster population as many of those owners have picked up a Model S. Still, it’s interesting how similar the RAV4 EV, LEAF, and Roadster populations are in how many miles they drive.

However, Model S owners are driving their cars substantially more. When comparing to the LEAF and RAV4, the Model S and Roadster have approximately the same range capability. Perhaps it’s the availability of Supercharging, the increased passenger and cargo space, or differences in the ownership demographics, or a combination of all three, that is enabling the Model S owners to drive well above the annual average for gas cars.

Stay tuned for more results as we continue to gather information from the EV owner communities. If you are driving one of the survey models, please visit the battery survey page to get more information and contribute your electric driving experience.

7 comments on “Battery Study Updates”
  1. Brent B says:

    This is great, but I am wondering if anyone has done anything since this to illustrate what happens to batteries over a greater time period. Also wondering about the impact of infrequent charging or frequent small charges on the life overall. I am in a bit of a bind as my lease is up on my Rav4 EV, which has been a great car minus an airbag cover issue. I have over 60,000 miles on it in 3 years and only see an impact on charging when it gets coldish here. I am considering buying one from a private seller with few miles but worry that it actually has a worse long -term viable battery life given how little it has been driven.

    1. Tom Saxton says:

      The Roadster began deliveries to customers in the fall of 2008, so we have data on vehicles that are coming up on 8 years old. The Leaf began deliveries in December 2010. Both of those are older than the new generation RAV4 EV.

      See the Roadster and Leaf charts for information from the current survey data.


      The survey collects information on charging habits, and the full data set is available if you’d like to do an analysis.

  2. dowen says:

    It would be interesting to understand if the SOC range has a meaningful impact to battery life. From the annual data – miles driven per year/divided by range (computed for Tesla 85S) it appears the typical discharge is from 100% to 83%.

    Is this a reasonable conclusion? Do most folks over the 17K driving miles recharge daily and typically have the same SOC?

    Is some of the variation due to folks driving to deeper discharge states?

  3. Brian H says:

    “that is enabling the Model S owners to drive well above the annual average for gas cars.”

    More like “the pleasure of driving it is motivating …” 😉

    1. jstack6 says:

      I don’t see a FORD Focus EV battery results. Mine has liquid cooling but it doesn’t work if you are parked and not plugged in. Phoenix heat seems to have taken 10% of my capacity in just 6 months over the summer. This is not good.

      The few FOCUS EV’s dealers had in the area are all sold out along with the plugin Fusion Energi and no new ones are coming in. Seems like a compliance vehicle so far. The heat issue could be big. Other liquid cooled batteries like the Tesla , RAV4, Honda FIT and Chevy Spark could have the same problems but I can’t find any in the area except the Tesla and 1 RAV4 EV. They won’t give us much data.

    2. Brian H says:

      What about the new Tesla-powered RAV4EV?

      1. Tom says:

        With 16 models of plug-in vehicles on the market and counting, and our limited resources, we can’t do surveys for all of them. For now, we are prioritizing open production vehicles available for sale in all 50 states that have some sort of instrumentation to allow the driver to evaluate battery pack capacity.

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