Tesla's Batteries are holding up well

[TonyWilliams]

Which is why unless we see statistics on Model S and Roadsters that lived in the AZ, TX regions for two years or more, with a minimum of 25K miles in it, it is meaningless to declare victory.

Others might be fooled, but Leaf owners need hard data that they can relate to.

Both Roadster and Model S are active cooled, so unless there is a failure of that system, the batteries are no worse off than a LEAF on the beach here in San Diego.

Or Steve's 80,000 mile LEAF in Kent, Washington.

 

[surfingslovak]

Which is why unless we see statistics on Model S and Roadsters that lived in the AZ, TX regions for two years or more, with a minimum of 25K miles in it, it is meaningless to declare victory.

Others might be fooled, but Leaf owners need hard data that they can relate to.

Jay, point taken. The Roadster study included a number of vehicles from AZ, TX and FL. The total number of miles driven was comparable to the LEAFs Tom evaluated earlier. I was at his TESLIVE presentation and asked couple of questions about the study. I think it's interesting and well done.

 

[tomsax]

The full write-up of the study results is available on the Plug In America web site:

http://www.pluginamerica.org/surveys/batteries/tesla-roadster/PIA-Roadster-Battery-Study.pdf" onclick="window.open(this.href);return false;

 

[tomsax]

Below is the latest graph showing the Roadster data (Standard mode ideal range miles) by odometer, grouped by climate (average high temperature). None of these Roadsters have had a full or partial battery pack replacement.

 

[tomsax]

The full data set is available from the Plug In America web site, but here's the relevant data from Roadsters still on their original battery packs and with sufficient information to get climate data, sorted by average high temperature high to low. Note that some of the cars in the hottest climates report never seeing the Roadster's hot battery warning, despite driving a lot of miles.

 

[TonyWilliams]

Tom, is "standard range" the same metric as "rated range" on the Model S ?

 

[qwk]

Tom, is "standard range" the same metric as "rated range" on the Model S ?

I think he used "ideal" miles coupled with standard charges.

The roadster "ideal" is not the same as "rated" in a Model S.

 

[mkjayakumar]

Though it is a limited set of data, the results are encouraging (compared to the Leaf). And also part of the equation is Roadster users don't end up cycling the charge as deeply and as often as Leaf owners.

But it is hard to believe that any TMS can keep the battery with a mass of 1000+ pounds, at a temp below 75F when the ambient highs are in 100F+ and lows barely get to high 80s for weeks on end (or months on end ?). So it is bound to have a significant impact.

 

[DaveEV]

Which is why unless we see statistics on Model S and Roadsters that lived in the AZ, TX regions for two years or more, with a minimum of 25K miles in it, it is meaningless to declare victory.

Others might be fooled, but Leaf owners need hard data that they can relate to.

Have you actually looked at the data?

http://www.pluginamerica.org/surveys/batteries/tesla-roadster/vehicles.php" onclick="window.open(this.href);return false;

Looks like the AZ vehicles are losing capacity faster than other states - about 10% after 2-3 years and ~40k miles. Not enough TX data to draw any conclusions.

Considering that AZ LEAFs are down about 20-30% after 2 years regardless of miles, it's pretty clear that Tesla's batteries are lasting much longer than LEAF batteries - about 2-3x better.

Even if you compare say a Los Angeles Roadster, those cars are showing about 5% loss after 2-3 years ~40k miles - again about 2-3x better than LEAFs.

Frankly, that's the type of capacity loss I was expecting in the LEAF and I'm highly disappointed that the my LEAF is doing 2-3x worse.

But it is hard to believe that any TMS can keep the battery with a mass of 1000+ pounds, at a temp below 75F when the ambient highs are in 100F+ and lows barely get to high 80s for weeks on end (or months on end ?). So it is bound to have a significant impact.

Well, it seems that Tesla lets their batteries get a bit warmer than 75F. But if anything, all the thermal mass makes it easier to keep the pack at a consistent temperature - as long as you don't let it heat up.

 

[tomsax]

Tom, is "standard range" the same metric as "rated range" on the Model S ?

For the Roadster, battery energy is stated in "ideal miles", an energy unit. 55 kWh = 244 ideal miles, so an ideal mile is about 225 Wh battery-to-wheel. The 244 miles comes from the Roadster's EPA rated range from 2008.

The Roadster has two primary charge modes: Standard mode and Range mode. Range mode is using the full usable battery capacity, Standard mode uses just the middle ~80% of the pack. So the best measure of a Roadster battery pack's capacity is the number of ideal miles shown after a full Range mode charge, but it's not as easy as you'd think to get that reading. Fortunately, the study shows and Standard mode ideal range and Range mode ideal range correlate very well. There's a more complete explanation in the paper.

The Model S can display current battery energy in two different units which differ by a scale factor: ideal miles and rated miles. Using the old EPA test cycle, the 85 kWh Model S would come in with a range of about 300 miles. So an ideal mile on a Model S is about 284 Wh. The new, more conservative, EPA test cycle gives the range of the 85 kWh Model S at 265 miles, from which rated miles are derived. 85 kWh / 265 rated miles makes a rated mile about 321 Wh.

Model S owners almost universally prefer talking about state-of-charge in rated miles.