Distraught by rapid loss of maximum battery storage

[T3slaOwner]

Amen. While I acknowledge that batteries degrade a bit over time, too many people worry over low percentage changes in the beginning. The op indicates about a 3% difference in the beginning. As you say, battery calculations just aren't that accurate, and there are several variables that affect it. Frankly, I am surprised they are as accurate as they currently are.

It's not really true to say "battery calculations just aren't that accurate". They measure the charge going into every cell and know pretty accurately how many kWh are in the battery at any given time. The range you will get is a different matter. So they typically err on the conservative side and often will get more accurate as the trip progresses. Sometimes they just plain mess it up. I've put maybe 22,000 on my car and only once did the projected range decrease to the point of impacting my trip. If I hadn't found a level 2 charger in a small town library, I might have had to push the car the last mile or so.

 

[Silicon Desert]

It's not really true to say "battery calculations just aren't that accurate". They measure the charge going into every cell and know pretty accurately how many kWh are in the battery at any given time. The range you will get is a different matter. So they typically err on the conservative side and often will get more accurate as the trip progresses. Sometimes they just plain mess it up. I've put maybe 22,000 on my car and only once did the projected range decrease to the point of impacting my trip. If I hadn't found a level 2 charger in a small town library, I might have had to push the car the last mile or so.

wont disagree with any of that. understand it well. point I am trying to make is that the op is expecting something more accurate and there are variables other than the battery that go into the mileage calculation.

 

[ajdelange]

This can get pretty confusing largely because Tesla isn't very forthcoming about the details of their algorithms. But it is clear that there are two kinds of range: estimated and rated. Rated is a fixed number which is really a proxy for energy stored in the battery. If any of the displays indicate a rated range of say, 200 miles and I know my rated consumption is .316 kWh/mi then I know my battery has 63.2 kWhr usable energy in it. If the battery display says it is 65% full then I know my full battery holds 97.2 kWh.

Battery calculations aren't that accurate. Were they accurate a battery history wouldn't look like this:

The reason it looks that way has to do with the estimation process. The observables are the time integral of the current pushed into the battery and the voltage change over that period of time. The voltage doesn't change that much with charge (unless you are at the tail ends of the range which is why they want you to go from well discharged to nearly fully charged occasionally) and so you get rated ranges of under 289 mi one fay and over 293 a day or 2 later.

The best way to see what your battery is doing is to examine plots like the one above over time and look for unusual trends. These pots are available from third party apps such as TeslaFi and Stats. Also keep firmly in mind that though the right axis, obtained by dividing the left axis by 295 and multiplying by 100, is and indicator of the rated battery capacity. That number is a constant and so the % values can be expected to trend down over time even though they may go up briefly. There is a chart in another thread that shows the history collected from a large number of cars. It shows up from time to time here and elsewhere. If you are way below the solid fit line and stay there, then you have a problem and a good argument at an SC. If you aren't, you don't.

 

[jboy210]

This can get pretty confusing largely because Tesla isn't very forthcoming about the details of their algorithms. But it is clear that there are two kinds of range: estimated and rated. Rated is a fixed number which is really a proxy for energy stored in the battery. If any of the displays indicate a rated range of say, 200 miles and I know my rated consumption is .316 kWh/mi then I know my battery has 63.2 kWhr usable energy in it. If the battery display says it is 65% full then I know my full battery holds 97.2 kWh.

Battery calculations aren't that accurate. Were they accurate a battery history wouldn't look like this:

View attachment 448358

The reason it looks that way has to do with the estimation process. The observables are the time integral of the current pushed into the battery and the voltage change over that period of time. The voltage doesn't change that much with charge (unless you are at the tail ends of the range which is why they want you to go from well discharged to nearly fully charged occasionally) and so you get rated ranges of under 289 mi one fay and over 293 a day or 2 later.

The best way to see what your battery is doing is to examine plots like the one above over time and look for unusual trends. These pots are available from third party apps such as TeslaFi and Stats. Also keep firmly in mind that though the right axis, obtained by dividing the left axis by 295 and multiplying by 100, is and indicator of the rated battery capacity. That number is a constant and so the % values can be expected to trend down over time even though they may go up briefly. There is a chart in another thread that shows the history collected from a large number of cars. It shows up from time to time here and elsewhere. If you are way below the solid fit line and stay there, then you have a problem and a good argument at an SC. If you aren't, you don't.

Agreed. I think people tend to associate it with fueling with gas which you can easily measure by sticking a stick in the tank or electronic equvalent (float system, capacitance gauges, etc.).

Battery charge is more difficult. Even measuring state of charge of a pack is at best an estimate using indirect techniques such as columb counting. And is effected by a lot of factors like internal and external temps, previous consumption rates, safety factors, etc. in relationships that Tesla probably knows, but does not publish and change over time. Also, some people seem to assume these factors are linear over time, when they are not.

 

[T3slaOwner]

Agreed. I think people tend to associate it with fueling with gas which you can easily measure by sticking a stick in the tank or electronic equvalent (float system, capacitance gauges, etc.).

Battery charge is more difficult. Even measuring state of charge of a pack is at best an estimate using indirect techniques such as columb counting. And is effected by a lot of factors like internal and external temps, previous consumption rates, safety factors, etc. in relationships that Tesla probably knows, but does not publish and change over time. Also, some people seem to assume these factors are linear over time, when they are not.

Not really so. The amount of charge going into the battery is easy to measure. The state of the battery is a bit harder but not so much. One problem is that there is energy in the battery which varies (even if no power is drawn by the electrics) with temperature. Another is that the amount of that power which can be withdrawn is a function of how you draw it. In other words, there are many losses in many places.

There are losses in the charging system which typically aren't important to the user unless he is being billed for the energy drawn from the grid and not what is delivered to the car. There are losses putting that energy into the battery. There are variable losses or gains in energy with changes in temperature of the battery. There are variable losses in drawing the power from the battery. Finally there are variable losses in using the power from the battery in the motor.

I would combine the losses in drawing power from the battery and the losses in using the power in the motor, but the amount measured is somewhere in between so the some losses show up in the energy measurement of usage and some don't. Whether they happen in the control electronics or the dashboard or the motor or the battery, I don't care except for the measurement point the car provides which is in between the motor and battery somewhere.

The user isn't provided with enough info to know where the losses are or even how much they are. But this measurement haziness is what we have to work with. Bottom line is we are not going to have as much knowledge about the state of energy in our EVs as we did the ICE vehicles we are used to. I was a chronic accountant and could tell you to within 10 miles how far I could get on a tank of gas as it neared the end. The many fewer opportunities for charging makes this much more important in EVs.

I'm concerned with the rate of degradation of the battery and there really is no good way to discern that. Even worse, it isn't guaranteed in the S or the X. If your battery goes to pot with only 50% range left, that's your problem. Makes sense. The cars that cost as much as a small house get no assurance the batteries will last. The cars that people pay not much more for than ICE vehicles get a real warranty on the battery. That is the sort of thing you do when the company is not headed in the right direction and ramping up the sales volume of the model 3 is critical.

 

[ajdelange]

Not really so. The amount of charge going into the battery is easy to measure.

Let's say it is doable with modern sensors and computing. One has to take the integral of the current over time and one has to use a Hall effect sensor as the current is DC and they do drift so that has to be compensated for.

The state of the battery is a bit harder but not so much.

The state is determined by a simple measurement of the open circuit voltage.

One problem is that there is energy in the battery which varies (even if no power is drawn by the electrics) with temperature.

Better to say that the energy available from a given charge level depends on temperature. True and that's why the Tesla's have a very sophisticated BMS that, among other things, maintains the battery at optimum temperature.

Another is that the amount of that power which can be withdrawn is a function of how you draw it. In other words, there are many losses in many places.

Energy that is "lost" when the battery is chilled is recovered when the battery is warmed. Of course it takes energy to warm the battery and so there is some loss from that but this is reflected in your Wh/mi reading and does not diminish one's ability to determine the capacity of the battery.

There are losses in the charging system which typically aren't important to the user unless he is being billed for the energy drawn from the grid and not what is delivered to the car. There are losses putting that energy into the battery. There are variable losses or gains in energy with changes in temperature of the battery. There are variable losses in drawing the power from the battery. Finally there are variable losses in using the power from the battery in the motor.

All of these are picked up in the Wh/mi calculation and do not effect the battery capacity calculation (well they do, of course, but not in a significant way).

I'm concerned with the rate of degradation of the battery and there really is no good way to discern that.

Yes, there is. It's pretty easy to determine battery capacity every time you charge (it's inversely proportional to ∂V/∂Q). From this one can monitor battery degradation over time and there are several third party apps that will do this for you. The graph in No. 23 is sample output from one of these programs (TeslaFi). It's a simple matter to see that my car was delivered to me capable of only 99.3% of its EPA rated range and though it went up to 99.6% for a while it has since declined to 99% in the 5000 miles I've driven it.


I think you are conflating two problems here. One is the decreasing ability of the battery to store energy as it ages and the other is the difficulty in knowing how much range one gets from a given amount of stored energy. While determining capacity of the battery isn't a trivial problem (that's why the data in No. 23 are so noisy) it is manageable to the point where we can draw meaningful conclusions from it. The other part of the problem is really the more difficult part. It is, in fact, impossible because we can't determine when we set out on a trip whether it will start to rain or if we will encounter a head wind. Even so I have found my Wh/mi predictions to be pretty accurate and stable and the trip energy monitor to be an extremely informative display

 

[Lloyd]

New owners need to expect 2-3% degradation in the first year. Its the nature of the batteries. After that about 1% per year or less depending on your charging habits.

 

[T3slaOwner]

New owners need to expect 2-3% degradation in the first year. Its the nature of the batteries. After that about 1% per year or less depending on your charging habits.

How about 4 to 5% the first year?

 

[mspohr]

I just posted the exact issue with my new Model X. Service advisor gave me the exact answer. Sorry, I don’t buy it. It’s all about the range game and marketing. I will continue to schedule service to bring up this issue until they come up with a software update to address the depleted range. It’s not about a defective battery, it’s about false advertising.

Do people sue ICE car makers when their cars don't meet the EPA mileage estimates?

 

[mspohr]

I just got my new Model X on June 21st and I am very happy with it with the exception of the rapid loss of maximum battery storage, and the unsatisfactory response from the service department.

When I picked up the vehicle, and for the first week, the maximum charge was 344 km, and not the official 347 km. Within a week it dropped to 343, then 342, and now the maximum charge is 334 km on August 21st. That is a reduction of 13 km in 2 months of new driving, which seems unacceptable to me.

I've contacted the service department twice, and both times was told that the maximum charge depends on my driving style, but this answer does not explain the lower than standard starting charge number, which is correctly set at the non-trip maximum. I thought all vehicles would have their batteries checked so that the battery level starts at optimum from the factory.

The reason why I am distraught is if the battery is defective from the outset, what will it be like after a year with the expected gradual deterioration of the battery over time? Although no issues have shown up on the vehicle's report to the service department, isn't this a warranty issue if the battery is defective from the outset?

Any suggestions?

Why are you charging to 100% so much of the time? Tesla says that's not good for the battery.

 

[T3slaOwner]

Do people sue ICE car makers when their cars don't meet the EPA mileage estimates?

They do if the cars are defective so they no longer would pass the EPA testing with the same mileage figure.

 

[T3slaOwner]

Why are you charging to 100% so much of the time? Tesla says that's not good for the battery.

Elon Musk posted information that showed the impact was minimal actually. But I want to say it was most apparent in the first year of driving. I believe that also included 0 to 100% charging.

 

[Pale_Rider]

They do if the cars are defective so they no longer would pass the EPA testing with the same mileage figure.

Except we’ve yet to see anyone drive their battery down, at anywhere near the EPA circuit speeds, to see just how far their battery can go. So far, all the complaints have been based on the highly variable “miles remaining” indicator on the dash.

 

[shinytop]

Ice makers have had to issue checks to users when EPA estimates proved to be inflated. I received a $750 check for my Ford C-Max. Funny thing I was getting the EPA estimate or better.

 

[ajdelange]

Yeah but how much did plaintiffs' attorneys get?

 

[VT_EE]

Do people sue ICE car makers when their cars don't meet the EPA mileage estimates?

The EPA mileage estimates apply to the vehicle when its new, not some time later after the batteries have slightly degraded. Everybody gets hung up on the static battery range indicator and act like that represents actual max range as defined in the EPA numbers. It isn't. You would need to run the vehicle through the EPA test sequence from start to finish to figure out whether or not you are can achieve EPA range. Unless you are seeing large, sudden drops in range, don't worry about.

 

[Lloyd]

How about 4 to 5% the first year?

That would be more than expected. See if it stabilizes there.

 

[T3slaOwner]

Except we’ve yet to see anyone drive their battery down, at anywhere near the EPA circuit speeds, to see just how far their battery can go. So far, all the complaints have been based on the highly variable “miles remaining” indicator on the dash.

Of course not. When you say "the EPA circuit speeds" they don't do goofy stuff to get arbitrarily good numbers. It is a mix of driving. The only thing unrealistic is the lack of use of heater or A/C, etc.

 

[T3slaOwner]

The EPA mileage estimates apply to the vehicle when its new, not some time later after the batteries have slightly degraded. Everybody gets hung up on the static battery range indicator and act like that represents actual max range as defined in the EPA numbers. It isn't. You would need to run the vehicle through the EPA test sequence from start to finish to figure out whether or not you are can achieve EPA range. Unless you are seeing large, sudden drops in range, don't worry about.

I see absolutely horrible numbers often. Trouble is the car doesn't really report numbers you can rely on. Let the car sit for two days and how many kWh is acceptable for it to drain away? I've never seen anything from Tesla. I had trips where the average Wh/mi was good, like 333 or less (better than the EPA numbers) and yet I couldn't go further than 200 miles without nearly running out of juice.

In my ICE truck I know how far I can go and there just aren't many variables that impact mileage significantly. In my X it seems like I have no way to know what to expect other than purely highway trips on a single day.

I don't really learn though. I don't like having to hit the brake in my truck every time I want to slow down even a little bit. Also even with a V8 it is rather underpowered. Just today I was thinking about what it would be like to have an electric truck. lol! it would be terrible unless they start building chargers at boat ramps and in the mountains along trout streams. The other thing I don't like about my truck is it's too large. I can't picture any EV company making a pickup that isn't a whopper! Both the Tesla and the Rivian are going to be full size, although the Rivian doesn't even have a six foot bed. It's more of an SUV with a place to put your dog... outside.

 

[T3slaOwner]

That would be more than expected. See if it stabilizes there.

It's not going to "stabilize". The curve never levels off, it just drops slower. In an ICE everything wears so you can expect them to last 200,000 miles plus with a few smaller parts breaking in the meantime (like starters/alternators, etc) and expected replacement of a few "wear" items like tires, battery, brakes. In an EV the motor and gearbox should hold up a very long time with the battery degrading steadily. Someone told me their battery cost $22,000 to replace (100 kWh). That's a lot worse than replacing a motor for $5,000. I expect people will keep their batteries until they are well worn, like 50%. But that will be 30 years or more for a typical owner.

As long as Tesla keeps charging my car for free, I'll keep running the charge out of it.