Tesla's 85 kWh rating needs an asterisk (up to 81 kWh, with up to ~77 kWh usable)

[flathillll]

The car's system is perfectly happy with reporting a full capacity of 81.x kWh, just as it was perfectly happy with reporting a maximum power of xxx hp (the precise number escapes me at the moment). Regardless of how these values are measured/calculated/estimated, if that's how Tesla chose to measure/calculate/estimate them, it's how they should advertise them.

You are still not getting it.... 81kwh ESTIMATE reported by the BMS is based on driving the car. if you simply parked the car and left the stereo on (or turned the car off because it is really always on) the battery pack would deliver more than 81kwh

the amount of Wh a cell delivers is dependent on the current, temp, and a few other factors

if you drove on the autobahn at 155 flat out the pack might only deliver 70kwh

 

[bridaus]

This thread would be greatly helped if we had an answer to how the 85 was calculated, even if it was just marketing mumbo jumbo (which I think is totally possible and no more or less slimy than any other car manufacturer). I still love my five acre plot (4.9), my 55 inch TV (not 55), my AC router that never reaches advertised speeds, and my Tesla. I only trust standardized testing and the resulting standard specifications. I know what I buy doesn't match what they say, I know I'm marketed to, and that's just fine. In the end, its just a number if you can't count it yourself by looking at it.

 

[Auzie]

You are still not getting it.... 81kwh ESTIMATE reported by the BMS is based on driving the car. if you simply parked the car and left the stereo on (or turned the car off because it is really always on) the battery pack would deliver more than 81kwh

the amount of Wh a cell delivers is dependent on the current, temp, and a few other factors

if you drove on the autobahn at 155 flat out the pack might only deliver 70kwh

Thanks, flat.

The car reports on a dynamic value that changes from second to second as it depends on countless also changing variables. Hence, it is impossible to have a single static specification that will precisely and accurately reflect that dynamic value in real world conditions.

All variables must be frozen (narrowed to a single number as well) to be able to precisely determine a multivariable dependent parameter. That is exactly how battery capacity is determined (all variables strictly defined and controlled conditions). It is impossible to do otherwise and misinterpretations and misunderstandings are common.

People expect to see the specified capacity number but they do not acknowledge or account for age and other variables that affect battery capacity

 

[dsm363]

The hard drive that came with a computer can be erased and used for full capacity if you wanted to. You can't do that with a Tesla battery pack.

Your EPA range rating comment shows that this is again very similar to the 691hp controversy. Tesla is (most likely) technically in compliance with laws/regulations/standards, it's just that these laws/regulations/standards are not what the consumers expect.

How exactly could you erase a hard drive in a computer and use it to its full capacity if the OS was on it and it was formatted?

 

[MP3Mike]

if you drove on the autobahn at 155 flat out the pack might only deliver 70kwh

Really? Do you have any evidence to back that up? (Besides the fact that it isn't possible.)

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The car reports on a dynamic value that changes from second to second as it depends on countless also changing variables. Hence, it is impossible to have a single static specification that will precisely and accurately reflect that dynamic value in real world conditions.

You state that as if it is a known fact... Do you have any evidence to back that up? (That the total kWh hour rating from the BMS changes from second to second.)

 

[Johan]

They are the same cells.
They dont use different cells in the different packs...
The killed the 60 and just so they could use the same modules and not the bastard modules with missing cells.
They didnt want to call it a 74kWh or 75kWh for marketing reasons ...
The 70 pack is underrated
the 85 pack is possibly a little overrated

Spot on. Let's all agree to disagree that it's hard to define exactly if the "85" pack holds anything between 77-85 kWhs - it depends on several different subjective choices in the way you measure and calculate the capacity. But, and this is important, it's deceitful by Tesla to not use the same principles when calculating and labeling their lower capacity packs (60/70) thus creating an illusion of a bigger difference between the different packs than there really is, in order to sell more of the bigger and more expensive packs. It's Tesla after all who have decided to use the kWh denominator of the packs to name their different models, and not for example the range.

 

[flathillll]

Really? Do you have any evidence to back that up? (Besides the fact that it isn't possible

Do you know what a hypothetical example is? Fine replace 155 flat out with "155 until the speed is limited and then continue to hold down the accel until you run out of juice" and the same is true.

anyone even remotely familar with lithium cells knows the capacity is inversely proportional to the discharge rate. the point is when you go really fast, not only do you get less range because of the air resistance (higher load) and the reduced motor efficiency, and blah blah blah; your effective battery capacity will also be reduced given the much higher than average discharge rate

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Spot on. Let's all agree to disagree that it's hard to define exactly if the "85" pack holds anything between 77-85 kWhs - it depends on several different subjective choices in the way you measure and calculate the capacity. But, and this is important, it's deceitful by Tesla to not use the same principles when calculating and labeling their lower capacity packs (60/70) thus creating an illusion of a bigger difference between the different packs than there really is, in order to sell more of the bigger and more expensive packs. It's Tesla after all who have decided to use the kWh denominator of the packs to name their different models, and not for example the range.

the spec capacity of the 85 pack is over 85 on a virgin pack

its is in no way deceitful to label the lower 60/70 packs different as if you drive a 85 and 60 pack at the same speed on the highway the load on each cell will be higher on the smaller packs. higher load mean faster capacity fade in the long term and reduced effective capacity when the load is being driven. also consider warranty concerns, smaller packs are much more likely to be range charged and more fully depleted more often than the large packs. try road tripping in a 60 or 40

 

[jcaspar]

So you got the increased range you wanted and you paid for but you are concerned that the battery rating difference may not be as much as advertised???

If you could magically have a 87KWh battery but it had the SAME range, would that put a good taste in your mouth?? Didn't you get every bit of the additional range you paid for? This seems to be the foolish part...

When I bought my car, I debated whether to spend $10,000 for the extra 15kwh (and the additional advertised range and acceleration) advertised on the 85 over the 70. At the time, I calculated that the EPA estimated range on the 85 did not represent an increase over the 70 that was proportional to the increase in rated battery capacity.

This puzzled me.

I knew that the additional weight from the cells should not negatively impact range to the extent predicted by the EPA range estimate, so it was unclear what was driving the discrepancy. In the end, I chalked it up to some oddity in the EPA test cycle. I knew that ICE manufacturers game the cycle with well tuned gear ratios for specific portions of the test, etc - so perhaps some aspect of their test is much more amenable to the 70 versus the 85. No one really puts that much faith in EPA mpg numbers anyways (only useful as a very loose comparison between cars) - so why would the rated range on an EV be any different?

In the end, I spent the extra cash on the 85kwh upgrade.

As a result of the findings in this thread, I'm convinced that regardless of whether or not the 85's 85kwh battery is "correctly" rated, it is "aggressively" spec'd relative to the 60 and 70 - to the extent that those that paid $10k for the 85 over the 70 received only 2/3rds of the bargain (~10kwh instead of 15kwh).

Personally, it leaves a bad taste in my mouth, and I'll certainly keep this experience in mind for the future. Fool me once...

 

[stopcrazypp]

The car's system is perfectly happy with reporting a full capacity of 81.x kWh, just as it was perfectly happy with reporting a maximum power of xxx hp (the precise number escapes me at the moment). Regardless of how these values are measured/calculated/estimated, if that's how Tesla chose to measure/calculate/estimate them, it's how they should advertise them.

I don't think any automaker would be able to follow that requirement. For example, every automaker is required to advertise the EPA range, however the range meter in the car does not have to follow this (some are a lot worse, like Leaf's guess-o-meter).

Also, I should say that the car never reports 81.x kWh. The car reports an estimate of usable capacity (that is the only number it can estimate) which people say are ~77kWh (which supposedly does not vary significantly with age/cycle which I find very weird) and then supposedly assigns a 4kWh number as a reserve. However, the car is never able to measure that reserve part (therefore it can't ever measure the true capacity of the battery). Unlike the Roadster, the Model S BMS does not allow you to go all the way down to absolute 0% SOC (2.5V).

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On the other hand, if the Tesla cell capacity are indeed overrated and the true capacity is indeed 81kWh, then there's no possible scenario under which you'll get 85kWh out of them, without altering the physical car as sold. You may say you can get 85kWh by pulling out the cells and discharging them at a certain rate down to 0V or something like that, but it's not possible to perform this in the car as sold, and therefore irrelevant to the average consumer.

This seems to be very similar to the 691hp debate. Sure there may be some way of achieving the rating, but not in the car as sold, and even the car's systems reports so.

This is talking about a different issue: usable capacity vs rated capacity. That issue affects all EVs. There is no EV out there that you can get the rated capacity out of it without altering the car, because they all use a smaller SOC window (90% or less).

 

[Auzie]

....................

The car reports on a dynamic value that changes from second to second as it depends on countless also changing variables. Hence, it is impossible to have a single static specification that will precisely and accurately reflect that dynamic value in real world conditions.

You state that as if it is a known fact... Do you have any evidence to back that up? (That the total kWh hour rating from the BMS changes from second to second.)

I did not say that the car BMS changes from second to second. I said it reports on a dynamic (changing) value.

The battery capacity is changing because it deteriorates with time, and it is dependent on a number of other ever changing variables. Battery capacity deteriorates with time whether the battery is used or not. If batteries are kept in strictly controlled storage and not used, they will lose some capacity due to self-discharge. If they are used, they lose capacity due to other factors as well. I think all this is common knowledge.


There are a couple of links if you are curious

Battery performance

Battery life


If the above is accepted as true, then it follows that the battery capacity specification (which is given as a single number for a new battery) will always be higher than the values that people can see in their cars.

It is unrealistic to expect the capacity specification to be for anything else but for a new battery.

 

[Johan]

So when a consumer is weighing whether to pay x extra dollars for pack B over pack A, should the way capacity of pack A and B not be reported by the same principles?

It's fine to up sell the larger pack by focusing on all its advantages: longer range, better performance, fewer cycles for the same amount of driving, more seldom need for range charging, etc. but in my opinion it's not fine to up sell the larger pack by using a different standard and/or rounding when stating its energy capacity as compared to the smaller packs.

It's a dollars to dollars comparison so it should be a kWh to kWh comparison too (not apples to oranges).

As stated before Tesla could have avoided some of this annoyance if they hadn't used the 60/70/85/90 numbers as such a core variable in describing their lineup.

 

[flathillll]

no. for all the reasons I already listed and because the reserve capacity (aka brick protection) is a larger percentage of a smaller pack

in any case Tesla's ONLY obligation is to spec the pack capacity at or below the capacity based on the cell spec

given it is spec'd 85 not 85.0 the pack could be as small as 84.5 and still pass muster, but like I said a virgin pack will deliver over 85 if all protections are disabled and you dischrage to 2.5v per cell given u used the spec charge, the spec discharge rate, & the spec temp

 

[Auzie]

So when a consumer is weighing whether to pay x extra dollars for pack B over pack A, should the way capacity of pack A and B not be reported by the same principles?

It's fine to up sell the larger pack by focusing on all its advantages: longer range, better performance, fewer cycles for the same amount of driving, more seldom need for range charging, etc. but in my opinion it's not fine to up sell the larger pack by using a different standard and/or rounding when stating its energy capacity as compared to the smaller packs.

It's a dollars to dollars comparison so it should be a kWh to kWh comparison too (not apples to oranges).

As stated before Tesla could have avoided some of this annoyance if they hadn't used the 60/70/85/90 numbers as such a core variable in describing their lineup.

I am curious, how would you line up the models? Make sure no one gets annoyed...:wink:

 

[Johan]

I am curious, how would you line up the models? Make sure no one gets annoyed...:wink:

They could be designated by EPA range, or they could be called Model S (formerly 60, now 70), Model S R (R=range, formerly 85 now 90) and Model S P. For example. Or they could be the Model S Azure, Comanche and Apache for all I care.

 

[Auzie]

They could be designated by EPA range, or they could be called Model S (formerly 60, now 70), Model S R (R=range, formerly 85 now 90) and Model S P. For example. Or they could be the Model S Azure, Comanche and Apache for all I care.

Your proposal fails annoyance test

Many people might object to those as too racist, or not diverse enough

 

[Johan]

Your proposal fails annoyance test

Many people might object to those as too racist, or not diverse enough

Yeah, base, range and performance are heavily loaded terms.

 

[cynix]

How exactly could you erase a hard drive in a computer and use it to its full capacity if the OS was on it and it was formatted?

You could boot it via a Live USB, for example. The point is that it's easily doable without any hardware modifications to the computer itself.

 

[cynix]

Tesla's 85 kWh rating needs an asterisk (up to 81 kWh, with up to ~77 kWh usa...

You are still not getting it.... 81kwh ESTIMATE reported by the BMS is based on driving the car. if you simply parked the car and left the stereo on (or turned the car off because it is really always on) the battery pack would deliver more than 81kwh

the amount of Wh a cell delivers is dependent on the current, temp, and a few other factors

if you drove on the autobahn at 155 flat out the pack might only deliver 70kwh

You can't expect me to buy a 200k car (yes it's over 200k here in Australia) and use it as an expensive radio. Since the EPA testing cycle is supposed to represent a "typical" driving load, they could simply report the usable capacity under that cycle. Or whatever testing standard that's applicable in the country of sale.

 

[flathillll]

You can't expect me to buy a 200k car (yes it's over 200k here in Australia) and use it as an expensive radio. Since the EPA testing cycle is supposed to represent a "typical" driving load, they could simply report the usable capacity under that cycle. Or whatever testing standard that's applicable in the country of sale.

yeah too bad the only global standard is to state the spec capacity. you could mandate all cars state the usable capacity at 65mph (since usable capacity is speed dependent for more reasons than one) but wouldnt it be simpler to state the range at 65mph and then have customers use that value when shopping?

in my industry we have tried to move away from specs and only state performance but you cant win and competitors will claim u have something to hide. people demand specs as that is how they have been trained to think by the suits

 

[Auzie]

Yeah, base, range and performance are heavily loaded terms.

I am glad we agree