Tesla Motors current and future battery degradation warranty...

[omarsultan]

So, thats not quite how the limited battery warranty reads. It covers you for a malfunctioning or defective battery (i.e. a sheet does south) but it does not cover you for the normal degradation of the back as it ages and you drive. I know your example is extreme to make a point, but I think it would be hard to get to 50% loss of range in 12 months without something being actually wrong with the battery.

My guess is they have a slope mapped out based on the 50K batteries in service and can identify the outliers based on devotion from the predicted slope. Whether they feel comfortable converting that into policy is the question. From a marketing perspective, you want the threshold to be high (we guarantee 90% of capacity after 5 years) but you need to balance that against the financial impact of the warranty liability you are creating.

I am fine with their apparent strategy of dealing with it if and when it becomes an issue.

 

[JRP3]

I'm posting because some members may be fooled into thinking that the Roadster is in someway substandard.

In fact the battery pack is substandard compared to what is being offered today in the Model S. The Roadster pack was built using off the shelf LiCo chemistry, the Model S pack is built using more advanced and durable NCA chemistry. Roadster chemistry cycled to around 500, S chemistry 2000+. They are vastly different, with vastly different expectations.

I tend to think that the Roadster does not have as good of a battery as the Model S.

No question about it.

 

[apacheguy]

3. One portion of the pack (e.g. sheet) can degrade prematurely. This effectively limits the capacity of the rest of the entire pack, due to the strings all being connected in parallel and min/max voltage levels. This is more of a judgement call - when is the degradation so great that the sheet can be considered "defective".

Right, and this is how I would approach a degradation warranty. I'd say if a certain sheet is 10% below the average of the other sheets then it should be replaced. However, I don't know how evenly the sheets degrade. If, for example, out of 10 sheets 9 reported a consistent capacity and 1 sheet reported 5% less then the others than I would also expect a warranty repair for that one sheet.

 

[yobigd20]

AFAIK Tesla's "internal policy" is that their warranty doesn't cover "natural degradation" but it does cover "unnatural degradation" bc that signifies a defective battery pack and the number they use is that if the battery goes below 70% capacity within 8 years that is unnatural and would qualify for replacement.

 

[richkae]

That's an exaggeration. Look at the Plug-In America graphs. They tell the story. Given the battery technology being used, there's no way the pack would degrade to 50% after 12,000 miles. It's simply not going to happen unless the pack seriously malfunctions, and that would be covered by Tesla.

Yes it is an exaggeration. I was trying to make a point. You say it is not possible, but if it did happen Tesla would cover it. I agree they probably would - but the warranty doesn't say they have to.
The Plug-In America Roadster survey only has data from 99 cars that did not have their packs replaced in it. 99 data points doesn't really give a lot of confidence. 19% of Roadsters in the survey have had their packs replaced. Maybe if all those packs had not failed the degradation numbers would be different.
My Roadster pack has been replaced twice. It is possible that it will fail again before I need to worry about range degradation. I love my car and I will pay to have it replaced *again* assuming that there are parts available.

We don't have hard numbers about the Model S other than we think it is "better".

Let's pick a different experiment. Suppose your range was down to 199 miles ( 75% ) of new.
What is the age ( and odometer ) after which you think Tesla should not replace the pack under warranty?

I know that is a hard question to answer without knowing all of the details that Tesla knows, but it is something I really want to be able to tell someone who I recommend a Tesla to.

- - - Updated - - -

AFAIK Tesla's "internal policy" is that their warranty doesn't cover "natural degradation" but it does cover "unnatural degradation" bc that signifies a defective battery pack and the number they use is that if the battery goes below 70% capacity within 8 years that is unnatural and would qualify for replacement.

Wouldn't people feel more comfortable buying if they had that in writing?

 

[AEdennis]

...Wouldn't people feel more comfortable buying if they had that in writing?

As well as to those of us that did buy.

 

[apacheguy]

AFAIK Tesla's "internal policy" is that their warranty doesn't cover "natural degradation" but it does cover "unnatural degradation" bc that signifies a defective battery pack and the number they use is that if the battery goes below 70% capacity within 8 years that is unnatural and would qualify for replacement.

IMO, that policy doesn't make sense. What if one were to lose 15% capacity in two years? Are you saying the owner would have to wait another 2-4 years for the warranty to be triggered? It needs to be "prorated" in some way.

 

[JRP3]

We don't have hard numbers about the Model S other than we think it is "better".

Not entirely true. We have test data from Panasonic showing the cell chemistry full cycling 2000+ cycles and we have a few Model S owners with high mileage and minimal range loss, some of which may simply be balancing/algorithm issues and not actual capacity loss.

 

[Lerxt]

It is clear that Tesla have to address this issue before Model 3 comes on line. I doubt people will buy the cars without some sort of assurance on range.

The best way to handle this will be
1/ set up a reasonably priced battery replacement program
2/ set a range/cycle/km threshold where beyond which the battery will be replaced, possibly with part owner subsidy
3/ set up a battery leasing system

If they don't do this I believe it is likely that a courtcase or consumer protection laws will force them into doing it. My belief is the leasing program is best. It cheapens the initial cost of the car and people are used to paying every month for petrol/gas so it's not a big stretch of the mind.

 

[yobigd20]

IMO, that policy doesn't make sense. What if one were to lose 15% capacity in two years? Are you saying the owner would have to wait another 2-4 years for the warranty to be triggered? It needs to be "prorated" in some way.

Yea I agree but because of the way battery imbalancing works and also because measuring actual capacity is impossible to be accurate, it's really hard to know for sure if your battery pack is really degrades or if it's just imbalanced or if it's just not accurate because you haven't done a single full cycle in years, etc. now try accounting for all that in a written policy. It's not easy. And I think Tesla's strategy here is just to defer for now and not talk about it so as to not draw attention to it.

 

[ch_model_s]

Not entirely true. We have test data from Panasonic showing the cell chemistry full cycling 2000+ cycles and we have a few Model S owners with high mileage and minimal range loss, some of which may simply be balancing/algorithm issues and not actual capacity loss.

Where are these 2000+ cycles always coming from??2000 cycles to 80%? with which DOD? i thought only lifepo4 can do this? do you have a source for that? every spreadsheet for the panasonic nca cells shows after 400-500cycles a remainig capacity of about 80%. Ok after that up to 2000 cycles it doesnt change that much. but fact is if you charge always to 100% you have 500 cycles with the standard chemistry to 80%. teslas custom cemistry is maybe a little bit better lets say 600-700 cycles to 80%. the trick is to charge it not often to 100% to give the customers a good enough battery life.

 

[ggr]

I'm pretty sure I remember signing a piece of paper during the ordering or delivery process for our Roadster (and similarly for the Model S), that acknowledged that I knew that batteries degrade and that normal degradation wasn't covered by the warranty. I'm traveling at the moment and don't have access to my copies of the paperwork, though. I know that we've all been trained to "click through" a lot of stuff like this, but I still read anything on paper before signing it. Is this confabulation on my part?

 

[JRP3]

Yea I agree but because of the way battery imbalancing works and also because measuring actual capacity is impossible to be accurate, it's really hard to know for sure if your battery pack is really degrades or if it's just imbalanced or if it's just not accurate because you haven't done a single full cycle in years, etc.

Actually it's not that hard if you have access to the BMS logs, which Tesla does. Imbalanced or weak cells will show up quite clearly.

Where are these 2000+ cycles always coming from??2000 cycles to 80%? with which DOD?

Page 20 http://www.embedded-world.eu/fileadmin/user_upload/pdf/batterie2011/Sonnemann_Panasonic.pdf
80% to around 1000 full cycles, discharging to 2.5V, which never happens in a car, 75% at 2000 cycles, and 70% isn't reached until over 2600 cycles. 1000 cycles on a 260 mile pack is over 200,000 miles even taking capacity loss into consideration.

 

[arg]

Here's my idea on this, but it requires a completely different thinking process in terms of predicted range.

(... hiding a reserve of range so that accessible range is always constant ...)

This is an interesting approach, but an expensive one: most cars will be driving around with a large reserve that's paid for but never used, while the 'outlier' cars will burn through their reserve in an exponential fashion (the more they degrade, the deeper they have to cycle the remaining capacity to keep the advertised range). Obviously it could be made to work with a large enough reserve, but is that price too high to pay? It also has the disadvantage of giving owners no benefit if they treat their cars nicely.

I'm also unconvinced that the problem is solved by more tightly defined warranties: if the warranty is going to state percentages, they are always going to have to be pessimistic: we will never have really good data to define the expected degradation in advance (before we have real historical data for any generation of technology, it will already have been superceded, and cycles of new technology are likely to continue for the forseeable future). So at best it's a bottom limit well below the 'expected' level, and the advantage for the consumer of being able to enforce a repair below the threshold is is offset by the disadvantage that manufacturers would probably be less likely to exercise discretion on the other side of the limit - if the limit is say 30% and you have a car at 29%, they are likely to say 'come back when it hits 30'.

I think that the underlying problem - of consumer confidence in batteries - is better solved by having more transparency on out-of-warranty repair costs. If you are able to obtain a replacement pack at any time for an published price (perhaps several published prices for new/refurbished-high-capacity/lightly-refurbished-poorer-capacity) and published trade-in allowances for packs in various conditions, then at least the costs are understood and (hopefully) manageable. With higher-volume vehicles, third party shops should be able to get into the refurbishment business, or even just the brokering business - taking degraded batteries from people who can't manage with the reduced range and selling them to people who need a cheap car without so much range.

 

[richkae]

Not entirely true. We have test data from Panasonic showing the cell chemistry full cycling 2000+ cycles and we have a few Model S owners with high mileage and minimal range loss, some of which may simply be balancing/algorithm issues and not actual capacity loss.

With 20x as many Model S on the road as Roadsters ( and the ability to drive much longer distances via supercharging ) there should be a much wider variance of results. A handful of outliers doesn't really tell you much without a proper survey.
Tesla could be using the telemetry data to identify batteries experiencing early range loss and replacing them, so that only they know the actual performance.

That would be great, I want them to replace batteries that experience early capacity loss. So why not have transparency and put it in the warranty?


I'm going to point out again that I have 2 Teslas and I plan to keep buying them. I chose to buy without a degradation warranty. I think that when Tesla wants to expand their market they may need to address it.

 

[JRP3]

Time will also solve much of this. If the packs behave the way I expect there will be plenty of examples of high mileage cars 2-3 years from now with minimal capacity loss and no examples of unexpectedly high capacity loss.

The problem with putting a specific number in a warranty is that number will have to be lower than the average expected loss, which will make pack durability look worse than it actually is.

 

[Johan]

This is an interesting approach, but an expensive one: most cars will be driving around with a large reserve that's paid for but never used, while the 'outlier' cars will burn through their reserve in an exponential fashion (the more they degrade, the deeper they have to cycle the remaining capacity to keep the advertised range). Obviously it could be made to work with a large enough reserve, but is that price too high to pay? It also has the disadvantage of giving owners no benefit if they treat their cars nicely.

I'm also unconvinced that the problem is solved by more tightly defined warranties: if the warranty is going to state percentages, they are always going to have to be pessimistic: we will never have really good data to define the expected degradation in advance (before we have real historical data for any generation of technology, it will already have been superceded, and cycles of new technology are likely to continue for the forseeable future). So at best it's a bottom limit well below the 'expected' level, and the advantage for the consumer of being able to enforce a repair below the threshold is is offset by the disadvantage that manufacturers would probably be less likely to exercise discretion on the other side of the limit - if the limit is say 30% and you have a car at 29%, they are likely to say 'come back when it hits 30'.

I think that the underlying problem - of consumer confidence in batteries - is better solved by having more transparency on out-of-warranty repair costs. If you are able to obtain a replacement pack at any time for an published price (perhaps several published prices for new/refurbished-high-capacity/lightly-refurbished-poorer-capacity) and published trade-in allowances for packs in various conditions, then at least the costs are understood and (hopefully) manageable. With higher-volume vehicles, third party shops should be able to get into the refurbishment business, or even just the brokering business - taking degraded batteries from people who can't manage with the reduced range and selling them to people who need a cheap car without so much range.

The problem here is that once degradation accelerates it really picks up the pace it seems. For example if I were to buy Kevin's car thinking it's good for me, since I never drive more than say 100 miles and can comfortably charge to only 80%, what if in just 50 or 100 cycles the battry degrades so quickly that I now can't even drive 100 miles?

 

[JohnQ]

Yea I agree but because of the way battery imbalancing works and also because measuring actual capacity is impossible to be accurate, it's really hard to know for sure if your battery pack is really degrades or if it's just imbalanced or if it's just not accurate because you haven't done a single full cycle in years, etc. now try accounting for all that in a written policy. It's not easy. And I think Tesla's strategy here is just to defer for now and not talk about it so as to not draw attention to it.

But we do have a way to measure actual capacity with a reasonable degree of accuracy. If I do a 100% charge, then drive down to or around 0 miles, I have a gauge on my screen that tells me how may kWh I used. That's the usable energy in my pack. I don't care if I drove 250 miles or what my avg Wh/mi is. If I do that 3 times in a row (say, on a road trip) then there's a degree of confidence in the number. I can then compare my number from last year to my number from this year and measure true degradation.

This assumes two things: 1) the zero mile point is set consistently across firmware releases which is not strictly true. 2) The pack is reasonably balanced. I have my energy numbers from November of last year, April of this year and will do a similar measure in about a week. Should give me a sense of true losses.

Measuring this way eliminates the issue of not fully charging and discharging regularly to "calibrate" the rated miles algorithm.

 

[Johan]

A full cycle is the gold standard method for capacity measuring and hence for measuring degradation. But it takes time and wears on the battery.

How about if voltage sag on load is highly correlated with total pack capacity?

 

[SebastianR]

Page 20 http://www.embedded-world.eu/fileadmin/user_upload/pdf/batterie2011/Sonnemann_Panasonic.pdf
80% to around 1000 full cycles, discharging to 2.5V, which never happens in a car, 75% at 2000 cycles, and 70% isn't reached until over 2600 cycles. 1000 cycles on a 260 mile pack is over 200,000 miles even taking capacity loss into consideration.

This! I think this debate is all a bit too excited for my taste: For whatever reason people seem to be very nervous about batteries and ignore that there are many things in an ICE car that break easily in the first 200k miles and typically mean the end of the car: transmissions/clutches, compressors and even breaks / faults in the break system often are more expensive to fix than buying a new car if you are beyond the 100k miles mark.

Tesla is clear that actual faults are dealt with under warranty, so there is no need to worry about the batteries as even a very unlikely "worst case" of driving +650.000 miles battery pack capacity (>70%) would leave you wit more juice in your pack than Nissan guarantees.

Now please don't bash me but if you want to worry about replacing something for the Model S, I would focus my worry on tires - with so much performance packed in the car some people find themselves replacing them rather often... :biggrin: