Model S fan builds database of battery degradation data

Tesla Model S

Batteries do degrade over time, and unfortunately most EV models haven’t been on the road long enough to provide a lot of data, so there is still much to be learned about how quickly capacity loss takes place.

Plug In America has conducted battery longevity studies for the Nissan LEAF and Tesla Roadster, and is in the process of doing the same for the Model S.

RELATED: Tesla Roadster battery longevity exceeds projections

In the Netherlands, Tesla enthusiast Merijn Coumans is working on a parallel project, updating a file of owners’ data on a regular basis, via the Dutch-Belgium Tesla Forum.

Tesla Model S max range

In this figure, created by engineering professor Maarten Steinbuch, the percentage of range loss is shown on the vertical axis, with 85 kWh models in orange and 60 kWh models in blue. The horizontal axis displays the distances driven.

The collected data indicate that the rate of degradation starts out relatively fast, then slows down as more mileage is put on the car. After about 50,000 miles, the overall range degradation is about 6%. From that point onwards, range is lost at a rate of approximately 1% per 30,000 miles.

SEE ALSO: Tesla infinite-mile warranty will also apply to Models X and 3

However, Steinbuch notes that, “these equations are just for engineering ‘fun’: we have only a limited amount of data points, a limited max distance, and the individual capacity will depend also on (ambient) temperature, time, usage etc.”

Battery pack balancing will also effect the reported range estimation. If the cells are widely out of balance, the reported range could be lower independent of any cell degradation. One Model S driver reported a range increase of about 10 km after “several full charges combined with deep discharges,” which, theoretically, gives the cells an opportunity to be closely balanced.

“I agree [that balancing effects the range estimation],” said Steinbuch, “but it is the best we have, at least you could say that these numbers are a lower bound – i.e. the truth will always be better than these numbers!”


Source: Maarten Steinbuch
Image: hans-johnson/flickr
[Updated 2/4/15 11:30am EST to explain the limitations of this data.]

  • Scott Liscomb

    Good information. It will be interesting to see how these numbers speak to us over time. My understanding is that a Level 3 Fast Charger can reduce the life expectancy of a battery, as compared to a Level 2 Fast Charger. Is that true? The company I work for provides EV Charging Stations and the Level 2 has a longer charging time, but may better preserve the live of an Electric Vehicle Battery. Also, Level 2 charge point stations are more affordable for areas where people typically park for more than a couple of hours anyway. Read more…

    • ned_plimpton

      It depends very much on what exact chemistry of lithium-ion batteries we’re talking about. Some are more tolerable to high currents and high temperatures than others.

      There was at a lot of early discussion that DC fast charging could degrade Leaf batteries quickly, but there a few studies have shown heavy fast charging usages only has a marginal effect.

      I’m afraid that this is one of those myths that will stick around for a long time, like Prius batteries wear out and are useless after three years or that laptop batteries have a memory effect.

      My wife still lets her iPhone discharge fully before plugging it back in because she heard its good for the battery. Even though I’ve tried to explain, over and over, that early Laptop and iPod batteries had a memory effect. They quickly changed the chemistry and it hasn’t been a problem to over 10 years…

      • tipoo2

        And now, in fact, deep discharges are what’s bad for your wife’s battery! Lithium Ion batteries are least stressed in the middle ranges, say 40-90%. That’s why electric cars often over provision their batteries with capacity that the user can’t use, so it’s not actually hitting 0% charge when the user sees 0% charge.

        Some Sony laptops also let you set a bottom percent for the battery to report as depleted, as well as a top percent.

  • jstack6

    Temperature is the biggest factor in any battery life and capacity I have seen. Fast Charging and Super Charging (Tesla only) can make the battery warmer. The chemistry of the battery is also a factor. With so many different designs and cells real life data like this study are very helpful.

    I’d mainly watch temperature and be sure any vehicle has a battery cooling system so you get the most out of your vehicle. A few companies make units that can monitor that data from the OBDII port. SCAN GAUGE , Leaf spy pro and maybe a few others. I use them and it is well worth the money to get that data.

  • dogphlap dogphlap

    While it is true that higher temperatures are not good for battery longevity and high charging currents produce heat that is not the whole story. From what I have read there are some processes going on during charging that reduce battery capacity that are time dependent i.e. if you charge at 2Xamps the damage due to those processes will be half that which would have occurred at Xamps simply because the charge will be shorter. There are other processes where degradation increases with current. So from a practical point of view the best option is to follow the manufacturers recommendations and hope they are motivated by truth rather marketing concerns.

  • dogphlap dogphlap

    Since Tesla cars are on line to the factory via the mobile phone network I wonder if TeslaMotors has this information for all the Model S cars so far delivered. If they do they could produce some awesome graphs with 50,000+ data points rather than the <100 here. With so much data it should be possible to extract the affect of frequent super charging and depth of charge or discharge for the cells they use. Anyway thanks are now due to professor Steinbuch.

  • Steven Alcorn

    Charles, As always, great article, and kudos to dogphlap for suggesting that Tesla may already have the necessary data. For all we know they are already analyzing the degradation data and updating the charging algorithms accordingly. Long story short, it seems that degradation does not seem to be a significant concern. Great to hear.