Battery Degradation and Tesla’s “Warranty”

[The original version of this post was written as a response on forum a few days ago.]

All EV batteries degrade. The important thing is to warrant what is acceptable degradation and what is not. Lacking the guidelines sucks, for lack of a better word, but it isn’t fatal. It’s just part of the equation.

We own our two Teslas and I am disturbed by Kevin Sharpe’s Experience, but the published guidelines did say 30% in five years… All this means is caveat emptor.

Our Roadster was already five years old when we bought it, so, I would love to know what I get with the CPO Warranty or what we would get with purchase of the 400 mile upgrade batteries. How long will the car run up to 400 miles.

On Twitter, Nikki Gordon-Bloomfield (@aminorjourney), has postulated that battery packs are the consumable portion of EVs.

Like it or not, she has a valid, and yet expensive point. However, unlike gasoline/petrol we don’t have to replace every time we charge, only as long as the batteries are useful for us. In which case, it’s eventually time to change.

Tesla’s Roadster warranty had defined that in a binary situation, so, if one were to make the case to swap it out under Tesla’s warranty, it can’t be done based on degradation, it is because of a full battery/system failure. This sucks, unfortunately that is what was warranted.

Now the valid question for Model S owners (and guess what, I’m one of those too) is what about our battery packs? Well.. We’ll need to see if degradation is covered.

[This is where new information, or should I say OLD information was posted on the Model S Warranty (including the current “unlimited” Model S warranty) also specifically excludes battery degradation. As was pointed out on both and forums, see page 35 and 36 (pages marked 33 and 34 due to other unumbered pages) of this PDF.

The particular language excerpted from the PDF link above:

“The Battery, like all lithium-ion batteries, will experience gradual energy or power loss with time and
use. Loss of Battery energy or power over time or due to or resulting from Battery usage, is NOT
covered under this Battery Limited Warranty. See your owner documentation for important
information on how to maximize the life and capacity of the Battery.”]

Otherwise, prepare to save for a replacement battery pack in the future. I have always recommended (often in the early years of my blog and in forums) that new EV owners put aside half of what their “fuel” savings aside for the future need to buy a replacement pack IF they do as I do with most of my cars (and that’s keep them for a LONG while) (my hybrid garage has a 2001 BMW X5, my non-green, I have to get to the mountains for Fresh Snow car.)

Guess what, that advice still holds. I’ve lost five miles of rated range from 265 max charge to 260 max charge. Ideal miles lost 3 miles. And I’m less than a year AND over 20,000 miles. However, it must be noted that Tesla delivered the car with greater than 300 miles of ideal miles and I’m just around 299-300 miles ideal now. Yes, it’s hotter in California than the UK and we do have active thermal management, but it’s still the case that degradation happens. I still made it to Barstow, then Vegas on SCs. The car is still awesome, the Roadster is still fun, and Tesla is not perfect. I never thought they were (if BMW i didn’t piss me off as much, I might still have picked up the i3 I ordered.)

[end of almost original forum post.]

After a day of mulling over the lack of battery degradation and comparing the Nissan Warranty, BMW’s match of said warranty and the fact that Tesla’s two competitors include battery degradation, I believe that it is time to call out Tesla and tell them that they need to include battery degradation into the equation. Spell it out. If it is the same specifics as the 2006 Roadster blog post that says 30% after five years, then that’s what it is. It’s not very impressive and I would ask that CPO Roadsters be provided with a modification to this, but that’s at least something. Additionally, AFTER providing such guidance, give us a price on replacement batteries. Nissan gave a $5,500 rate for their cars, why can’t Tesla do it now? With the pending Gigafactory, surely the economics only gets to improve.

C’mon Tesla, be awesome again!

6 thoughts on “Battery Degradation and Tesla’s “Warranty””

  1. A good analogy to change in battery capacity over it’s useful life cycle is tire tread. Over time a degree of wear is normal, but varies depending on driving conditions (road surface) and driving style.

    Typically tires have a minimum, or an expected life in miles. There are some conditions (if encountered) that can cause premature wear, or failure of a tire. Similar situations exist for batteries.

    While tires don’t effect range for each trip, they do have a total range. A better matched anology to EV battery capacity is race-car that need to re-charge tread a number of times to complete a trip.

    1. Great analogy Brian. I actually used tire tread on one of the forums (Kevin Sharpe’s been posting up a storm) as a way of measuring how Tesla could possibly credit owners for replacing or repairing sheets in their cars.

  2. While CARB does specify a range capacity be measured for certification, they do not specify what is an acceptable amount of range degradation, or a percentage of range capacity that needs to be maintained over the vehicles life. Only a service life in years and miles is stated warranty requirement.

    “Extended Warranty: Extend the performance and defects warranty period set forth in subdivisions 2037(b)(2) and 2038(b)(2) to 15 years or 150,000 miles, whichever occurs first, except that the time period is to be 10 years for a zero emission energy storage device used for traction power (such as a battery, ultracapacitor, or other electric storage device).”

    Part of the issue is CARB regulations is they were initially developed for Hybrids, then PHEVs (including EREVs & BEVx), for ensuring that the battery kept emissions in check. BEV battery warranty details got overlooked as BEVs are always ZEVs. (NEV do have stated capacity rating based on lead-acid chemistry degradation profile … not an useful match to modern EV battery capacity)

    However since range capacity effects amount of use over a vehicles life, we should expect to have a warranty stating a minimum usable capacity after 5, 10, or 15 years (and 100,000 or 150,000 miles). Ideally the minimum capacity would be a percentage of new battery capacity.

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