## Plug In America study projects Tesla Roadster packs will retain 80-85% capacity after 100K miles

##### 14 July 2013
 Capacity of Tesla Roadster batteries versus miles driven using the three types of capacity measurement: range mode (blue diamonds), standard mode (red squares), and calculated Ah capacity (green triangles). n=122. Source: PIA. Click to enlarge.

A study of Tesla Roadster user data published by plug-in vehicle advocacy organization Plug In America (PIA) projects that the battery packs in the Roadsters will retain 80-85% of capacity after 100,000 miles (160,934 km) driven.

The finding, released at the Teslive Tesla users conference (a partnership between Tesla Motors Club (TMC) and Tesla Motors), bests initial projections set by Tesla Motors in 2006 which suggested a 70% capacity retention after five years and 50,000 miles driven, said Tom Saxton, Plug In America’s chief science officer, who wrote the study.

 PIA projections of Roadster battery capacity after 100,000 miles using data (left to right) from its survey, from the subset of owners with the original battery pack, from the subset of owners with replaced battery packs, and with OVMS data. Source: PIA. Click to enlarge.

Unlike the results from the earlier Plug In America LEAF Battery Survey, the Roadster study found no significant correlation between climate and battery longevity. “Roadster owners in hot climates are not seeing noticeably different battery capacity profiles than owners in moderate climates,” said Saxton.

Plug In America launched the survey in January 2013, receiving data from about 4% of Roadster owners worldwide who completed a form on the PIA website. This was combined with anonymous data from OpenVehicles.com, an aftermarket vehicle monitoring system.

Deliveries of the Roadster began in 2008; 2,500 Roadsters were produced through the end of production in January, 2012. As of 4 July 2013, Tesla Motors reported that 2,100+ Roadsters have been driven more than 35 million miles.

Plug In America contacted Tesla Roadster owners via social media including the Tesla Motors Club and various other online groups and asked them to submit data for their vehicles. As of 5 July 2013, 126 vehicles totaling 3,198,749 miles had contributed to the survey, amounting to approximately 5% of the user base and nearly 10% of the miles driven as reported by Tesla Motor; of these, data from 122 were used for the full analysis.

In addition, data from 106 Roadsters was collected anonymously through the Open Vehicle Monitoring System (OVMS), with considerable overlap expected between the two data sets, Plug In America said. (OVMS data was from 106 owners who have installed the OVMS device and chosen not to encrypt their data.)

For the Roadsters analyzed, average miles driven was 25,387 (40,856 km); the median was 21,131 miles (34,007 km); and the most miles driven was 87,111 (140,192 km).

Of the 122 owners in the PIA survey, 23 (18.9%) reported that some or all of their battery pack—comprising 11 equal sheets of 621 cells—had been replaced. Replacement can range from a single sheet to the entire battery pack.

The study evaluated three different measurements on battery pack capacity: Standard mode ideal miles, Range mode ideal miles, and Calculated Amp-hour Capacity (CAC).

Tesla allows the owner to view the car’s estimate of the battery pack’s current stored energy in a unit called an “ideal range mile” (IM). The Roadster has two primary charge modes: range and standard. Range mode allows maximum charge and discharge, and thus maximum driving range. Standard mode charges to about 90% of the pack’s usable level and also hides the bottom 10%. Charging and driving within Standard mode protects the battery from both high charge and discharge levels.

The study found that standard mode IMs correlated very well with CAC; range mode correlated less well, with a few outliers both high and low, lowering the correlation coefficient.

The projections from the various data sets suggest that Roadster batteries will be at 80% to 85% capacity after 100,000 miles, on average, Saxton concluded—i.e., an average loss of about 3.7 ideal miles of range (1.6%) per 10,000 miles driven.

There is significant variation in battery capacity reported; the difference in capacity between vehicles with similar mileage can be as large as the projected loss over 100,000 miles of use. Individual owners should therefore expect variation between their experience and the projected average performance.

Because of the variation in battery pack longevity experienced by owners, especially where such variation may be due to factors beyond the owners’ control, it would seem desirable for the manufacturers of electric vehicles to guarantee not only the life of the battery pack, but also the capacity performance over time and miles. Nissan Motors responded to the climate issues reported by LEAF owners (and confirmed by the Plug In America study) by amending their battery warranty to cover capacity. With the performance of the Roadster battery packs exceeding early expectations, it’s curious that Tesla Motors doesn’t offer any capacity warranty, even on the 85 kWh Model S, which has a warranty good for 8 years and unlimited miles.

—Plug In America’s Tesla Roadster Battery Study

Studying the Nissan LEAF EV, Plug In America conducted the first evaluation of plug-in battery performance last year. The purpose of these studies is to help consumers better understand battery reliability, support industry-wide adoption of standard battery performance warranties, and inform consumers making extended-warranty purchase decisions. Andy Palmer, executive vice president of Nissan Motor Co., Ltd., encouraged every LEAF owner to read the survey’s results when Nissan announced the addition of capacity-loss coverage to an enhanced LEAF battery warranty.

Plug In America has also launched battery-pack performance surveys of the 1997-2003 Toyota RAV4-EV and the new Tesla Model S. The RAV4-EV survey will document the 10-year experience of owners of these early electric vehicles.

It is premature to glean much about battery capacity for the Model S, which became available in mid-2012, but this research has already shown that survey participants are driving an average of more than 16,000 miles per year, well above the national average of 13,500 miles for conventional vehicles, Saxton reported.

In addition to heading up Plug In America’s battery performance research, last year Plug In America conducted the first performance evaluation of public EV charging infrastructure effectiveness including charging station reliability, availability and average-use levels.

If true, this would mean the Tesla Roadster would still have a per charge range of 200 miles even after it's racked up 100,000 miles on the odometer.

Ouch!

An unbiased study by Kit P based on a survey of one concludes that my wife's Corolla will last forever. After 130,000 miles the engine is at 100%.

The problem with a survey is that people are reluctant to report FAIL.

@Kit P,
Indeed, in the hand of a master mechanical engineer, a Corolla can last forever.

Yet, a Corolla that formerly belonged to an University Professor, then later given to his college-age son, now at 120,000 miles, loses 1 quart of oil after a few hundred miles, had the catalytic converter replaced, and has vibration in transmission at certain rpm range or driving condition.

Most ICEV's belonged to non-mechanical owners will run ragged and suffer from frequent engine-related problems/failures after 150,000 miles. Most will trade in their ICEV's after 150,000 miles for newer cars because the cost of repair often exceed the value of the car.

One Honda Accord stil run strong on the original engine after 1 million miles, but the owner is a Honda mechanic who is able to maintain and fix his own car. Indeed, owners who understand about engines and cars and can fix them can make an ICEV run forever. In Cuba, American-made cars of 1950's vintage are still running strong, and they seem to last forever.

The same is probably true for BEV's. However, replacing electrical components of BEV's is very easy, and the electric motor is so simple that has nothing that can fail, provided that the car computer with sensors can protect the motor and battery from owner's abuses. Computers and electric components has mean time between failures (MTBF) of over 50,000 to 100,000 hours. Solid-state hard drives has MTBF in the millions of hours, vs spinning hard drive with MTBF of 100,000 hours.

@Roger

I do not work on my wife's car. I pay someone else to change the oil.

Roger is under the mistaken belief that an idiot who tears up a car with an ICE will not tear up a BEV.

My son's has been driving a 93' Camry that is older than he is for 4 years. It uses a half a quart in 5000 miles. As does my 89' Ranger which I have been driving to destruction for 15 years now. Maybe i should change the plugs and wires not that it showing any signs of needing a tuneup.

“The same is probably true for BEV's. ”

Roger maybe then you should wait to say in when it is true least we think Roger is a big fat lair.

@KP,

Your experience is not typical of the mass of motorists, to put it politely!

Another Camry that I know with under 100,000 miles, was originally owned by an elderly lady driven mostly from home to church and local market, got oil changed from quick-lube type of places...this vehicle consumes about 1 quart of oil every 500 miles or so ...It has got a starter failure at ~70,000 miles...It developed a sticky gas pedal and drive train noises...The engine thermometer has malfunctioned for a while, thus causing suboptimal operating temperature leading to engine deposits and more rapid engine wear in colder weather. Of course, a lay person does not appreciate this and continues to drive the vehicle.

The cars that I changed oil myself using only synthetic oil, and did all maintennce and repair, have zero oil consumption after each 7,000-mile oil change interval and run like new at nearly 100,000 miles. So, yes, in good owners who change their own oil with synthetic oil and drive carefully, ICEV's can last forever. Sadly, the durability of ICEV's in the general public has not been too good.
The reason for this is that ICE has many precision moving parts fitted together with high tolerance and lubricated with a thin layer of oil. If dirt gets into the engine during maintenance and repair, the engine will wear out very fast. Folks who do jack-rabbit acceleration on a cold engine, and who don't check their oil level, and take their cars to the shop under the care of careless mechanics...their cars don't last long!

BEV's and PHEV's, on the other hand, do not need oil change nor any maintenance on the power plant...No chance of dirt contamination and improper handling by careless mechanics. The car's computer can make sure that the motor and the battery do not get overheat, and can help ensure that the battery will not get overly drained nor over charged. In this way, BEV's and PHEV's will have much higher durability than ICEV's no matter who is the owner!

Since the vehicle controls the ultimate parameters of battery use most packs will see similar conditions. The study tracks the capacity of the pack. How is it not a valid study?

It is not a valid study because it is nIt is not a valid study because it is not an independent check of failure. It is not typical of group.
If I surveyed Toyota mechanics for the cost of labor for repairing their cars you would get skewed results. For many years I did not pay labor to fix my old POS. My wife carpooled my mechanics family since his wife did not drive and our boys were the same age in the same schools.
I asked another Toyota mechanics when the earliest he saw a timing belt fail on a PU. This is what I based replacing the timing belt rather than the owner’s manual recommendation.
It is very likely that paying a $100k would result in me learning how to make a BEV last a long time because I am not a typical driver. It is very typical for people to buy Corolla for about$16k and make them last a very long time. This is why they have high resale.
Cute and exotic gets boring very fast. How long they last does not matter.

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