Actually the problem was people were running the tank to "empty" or past empty and they could only fit X gallons in when the tank was supposed to hold X+6. So it said you were empty when in fact 20% of the fuel was still there but not usable, so not the exact same thing but similar idea.
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Infinite Mile Battery Warranty [Now] Being Honored By Tesla [Issue Resolved]
- Thread starter HMARTINPT
- Start date
Electric700
Active Member
This is really good news! I am happy to see that Tesla resolved the problem for you.
CAN bus data is not necessary to measure your cars battery capacity. Useable battery capacity can be fairly easily calculated on any Tesla by using the cars trip info. You need to use three numbers. State Of Charge (battery percent) at the beginning and end of a trip, and the "kWh used since last charge".
Start a trip after charging. Note the starting battery percent. At the end of the trip, note the battery percent and the "kWh used since last charge." Divide the kWh used by the change in battery percent (divide the percent by 100 to use a decimal amount). For example: battery starts at 80%. End of trip, 36 kwh used, and battery percent at 30%. The battery fraction used is 50%, 0.5. 36kwh/0.5=72kwh.
The advantage of this method is that it is independent of driving style and the cars questionable estimation of range. The trip used for this calculation should be as long as possible. From 90% or 100% down to some very low state of charge would give the most accurate measurement. But I have found that the SOC measurements are very linear.
Your car clearly had a battery with excessive degradation. I too was annoyed by those on the forum here who defended Tesla's refusal to replace the battery. They should have replaced it from the start.
The issue with this method is the displayed trip info kWh usage only accounts for energy used while the vehicle is in motion.
You’re correct though that you don’t necessarily need to read CAN bus data to understand your batteries max usable capacity. If you do a 100% charge, record the rated miles and multiply that by the EPA consumption rate, you’ll get the same value as the CAN bus data “Nominal Full Pack” value. There’s any entire thread on this here:
Calculate usable battery capacity based on rated miles values
You are "getting" 250 miles? Or the display is showing 250 miles? Big difference.
There is very very little energy used when the vehicle is not in motion. And a longish trip during one day has the car "On" or in motion pretty much the whole time.
The method you propose uses the cars display of range as a basis for calculation. This number is not reliable (it is certainly way off on my car). SOC and kwh used are accurate numbers and so are a better way to measure useable battery capacity.
That's funny you say that the displayed range number isn't accurate, but the SoC number is. They are the same thing, you can convert from one directly to the other.
The displayed range is the best way to determine degradation.
The displayed range value is calculated from SOC and some other assumptions. Specifically, an assumed wh/mile and useable battery capacity. If I am trying to measure useable battery capacity, it would not make sense to use a value which itself is derived from some other calculation of battery capacity.
So no, using displayed range to calculate battery capacity is not better, but is an inferior method. Better to use raw data - kwh consumed and the change in SOC.
Here is an example: I unplug the car and go on a little trip. The SOC display is 80% at the start. This is a very reliable value that is not derived from other values and does not include any assumptions. I take my trip. At the end I note two things. One, the SOC is now 30%. Again, a reliable value that is as close to raw data as we can get. I also note that the "kWh used since last charge" is 36 kwh. This also is raw data. Since it took 50% of my battery capacity (80%-30%) to provide 36 kwh, then 100% of my battery must be twice that, or 72 kwh (36/0.5). I have repeated this calculation on my car using a great variety of charge states and trip distances. The value for useable battery capacity always comes out to 72 kwh (+/- 1).
It's the best way. And it's easy. And it doesn't require charging to 100%, which we should avoid doing. The accuracy will be better if you do the calculations after trips that use a large portion of the battery.
Here is the formula:
Useable battery capacity equals (Kwh used) divided by ((SOC start minus SOC end)/100).
(You have to divide the SOC difference by 100 to convert % to fraction)
ucmndd
Well-Known Member
Rated range remaining and SoC are the exact same information represented in different ways.
SoC is available capacity divided by max capacity.
Rated range is available capacity divided by a fixed wh/mile constant.
Any calculation made with one can also be made with the other and they will yield identical results.
How much energy your vehicle consumes while not in motion is completely dependent on a number of things. In a cold climate, it’s not “very very little”.
Here’s a thread on why you won’t actually get the displayed rated range even if you drive at the EPA assumption: This is why you can't get 'rated range'
That being said, it’s been proven several times that you can get the same BMS reported nominal energy remaining at 100% SOC by taking the displayed rated miles multiplied by the EPA rating for your vehicle. For example, my displayed range at 100% SOC is 262. The EPA rating for the 85D is 290 Wh/rated mile. 262 * 290 = 75,980 Wh. BMS was reporting nominal energy remaining of 75.980 kWh. I’m not sure how you can claim this is unreliable when it’s matching exactly what BMS is reporting.
Edit: I should also note I was a “non-believer” before as well and thought trying to calculate the battery capacity from rated range was not accurate. Then I did the math, compared it to BMS reported values via the CAN bus, and they matched exactly. Several other people have done the same thing, and it matches exactly. Turns out my initial understanding was wrong, and I have no problem admitting that. Part of my flawed understanding was how much misinformation is out there.
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That is not quite true. At a given point in time, you can kind of use it that way, but over longer periods of time, that ratio doesn't stay constant, because the state of charge number is being represented as a %. Here's an example to explain. An original 2014 S85 stated with a rated range number at 265 rated miles. When new, you could flip the display back and forth and see 265 rated miles or 100%. A couple of years go by. It holds a little less energy, and top rated range only goes to 255 rated miles now. But if you flip the display, it will still show 100% full, because that is the most it can put in the battery. Another couple of years go by. It now will only show 249 rated miles, but it will still show 100% when it's full. So it is not an exact conversion of those two numbers.
Yes--sort of. But it is "capacity" in terms of amount of energy--not in percent. So when you flip it to the rated miles display, it is looking at the amount of energy it has (kWhrs) and converting that by the fixed wh/mile constant. But the % value is still more like how full it can get of the total amount it's able to use now. So that supposed equation of percent to rated miles can shift as the total amount of usable energy that makes up a full 100% battery shifts over time.
You are both correct because you are talking about two different things. You are correct that usable energy, as defined by wk057, is calculated by .295 x 265 = approx. 78 kWh usable, for the original S85 when new. This is correct because if you drove the car from 100% to 0%, you would have to add back 78 kWh to the battery to get 100% recharged, i.e., 265 rated miles x .295 kWh/mi to fully recharge the car. This also does not include the energy buffer (at least very little of it), since you stopped at 0% SOC remaining.
However, not all that energy is useful, as in available energy to propel the car, and that is what Peter Lucas is describing by his method. So, if you charged to 100%, and took a continuous drive to 0%, you would only get about 74 kWh used displayed on the dash, which is going to be accurate assuming negligible unreported losses due to any energy usage while not moving. Any long stopping periods, of course, would cause an unreported error in that value. And as he stated, you don’t need to use 100% of the battery to calculate this, just take kWh reported used divided by % SOC used, from a continuous drive.
So actual battery capacity really depends on what exactly is being defined, as the difference in these two methods is not negligible, as in this case, which is about 5%.
For my car, it is about 6% difference between what it takes to charge vs. what I will actually get when driving.
The display is at 250 miles with 100% charge. Trust me, I know the difference.
Dr. J
Active Member
Now THAT, my friends, is how a TL;DR is DONE!What an entertaining thread from beginning to the end, lol.
Beginning: OP was YELLING at us about his frustration, lol.
Middle: Ridiculous debate about the battery and how 10% degradation over a few weeks is normal
End: A happy ending with OP getting the new battery he deserves
Waiting on that Easter egg: What exactly was the fault?!
As a #tbt to the how the OP posted: GLAD TESLA IS REPLACING THAT BATTERY OF YOURS! ENJOY!!!
I am having the same problem and getting the same canned responses from Tesla...it’s extremely frustrating. However mine is not as bad as yours. I have 64,000 miles and have a 9% degradation loss. The main problem I am having is that 5% degradation occurred within the past 3-4 months ago. They told me the same story. I am so frustrated with Tesla’s lake of concern that I don’t enjoy driving the car anymore.
Have you mad any progress since you’ve posted this?
might want to joint this tread...tons of people with same problem
Sudden Loss Of Range With 2019.16.x Software
That 5% from 4 months ago is not degradation. It is the result of 16.1 software capping your capacity. It's still there but Tesla won't let you use it.
So glad I'm still on v8.
i asked Tesla to confirm if any software updates reduced the capacity, and, like I thought, they would not confirm it.
From what I read Tesla reduced the charging capacity because of the batteries that caught fire. If this is accurate, there’s a defect in the battery and should be replaced under warranty.
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