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No battery degradation??

MY-Y

Member
Mar 4, 2020
969
1,061
MD
Not true.. When you adjust the charge level slider to 100%, the max estimated range is displayed, nothing more. The difference between advertised max range and this estimate is not how you understand the health of the battery, period.
That's commonly said on this forum, but that is not my experience.
For my car right now...
Sliding to the right: 289 miles
Scanmytesla (reading what the BMS thinks): 287 miles

Using estimated range for the degradation calculation: 287/326= 88% of its original capacity.

The original capacity is 77.8kWh (also reported by the BMS), so using the range estimation for battery health calculation shows my current capacity is 0.88*77.8 = 68.5 kWh. What does the BMS say? The BMS also says 68.5 kWh.

The slider range estimate is within 1% of what the BMS is reporting. This is what the BMS uses for battery capacity (a.k.a. battery health).

From what I see, you can observe battery degradation from the slider as well as the BMS can see it.

Screenshot_20210524-163304_Tesla.jpg
Screenshot_20210524-163231.jpg
 
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Oct 3, 2020
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That's commonly said on this forum, but that is not my experience.
For my car right now...
Sliding to the right: 289 miles
Scanmytesla (reading what the BMS thinks): 287 miles

The BMS calculated degradation as 287/326= 88% of its original capacity.

The original capacity is 77.8kWh (also reported by the BMS), so using the range estimation for battery health calculation shows my current capacity is 0.88*77.8 = 68.5 kWh. What does the BMS say? The BMS also says 68.5 kWh.

The slider calculation shows degradation within 0.5% of what the BMS is reporting.

From what I see, you can observe battery degradation from the slider as well as the BMS can see it.

I take it that this is surprising to you? To me, it isn't. You're reinforcing the fact that the capacity that the BMS reports is what it thinks it has access to.

The ONLY way to truly know what it has in terms of available capacity is to drive it and do the math. Then, and only then, can you declare how much capacity/degredation you have.

Being that I have yet to hear of anyone taking the time to do a proper capacity/degradation test, those that are complaining about premature degradation need to stop jumping to conclusions by declaring something that they have no credible evidence to back up.
 
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MY-Y

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Mar 4, 2020
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No, it did not surprise me. I was demonstrating how the estimated range is a reasonable way to determine battery health by showing that is how the BMS does it.

I'd like to know how Tesla determines a battery is below the 70% capacity when making a warranty claim. Do they take the car's BMS' word for it, drive it and do the math, or use something else?

Tesla's own highly sophisticated BMS reporting my battery has lost 12% of its capacity seems like credible evidence to me. Why is driving and doing the math (using the same BMS to give the energy used) the proper way to determine degradation? Is that documented by Tesla somewhere?

I hope my tone is coming across as sincere and not argumentative. I don't like Internet arguments, and am just trying to share what I've learned and learn from others. I'd be very happy to find out my battery isn't actually down 12%.
 
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Oct 3, 2020
205
215
Seattle
No, it did not surprise me. I was demonstrating how the estimated range is a reasonable way to determine battery health by showing that is how the BMS does it.

How does Tesla determine a battery is below the 70% capacity when making a warranty claim? Do they take the car's BMS' word for it, drive it and do the math, or use something else?

Tesla's own highly sophisticated BMS reporting my battery has lost 12% of its capacity seems like credible evidence to me.

They run the battery through a series of tests and incorporate the CAC (calculated amp hour capacity) to evaluate battery degradation. Once again, this is yet another example of just how misleading your method is when it comes to understanding battery degradation.

To understand degradation, you must first recognize the difference between amp hours and kilowatt hours. Amp hours is a measurement of battery capacity, while kilowatt hours is a measurement of electrical power. Being that watts are used to describe the power that's involved to do work, and amps are used to describe electrical energy, it should become more clear as to why understanding battery capacity is not as easy as many appear to think.
 
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SigNC

Active Member
Aug 23, 2017
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I baby my MY battery, and in 11 months, and 12k miles, I dropped from 326 to 283. Some just do poorly (like mine) and some do well. I'm almost half way to qualifying for a battery replacement. Hopefully it flattens out soon, or keeps falling to 228 (new battery).
almost surely not actual degradation and more likely your charging habits are throwing off the BMS.
 

MY-Y

Member
Mar 4, 2020
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MD
They run the battery through a series of tests and incorporate the CAC (calculated amp hour capacity) to evaluate battery degradation. Once again, this is yet another example of just how misleading your method is when it comes to understanding battery degradation.

To understand degradation, you must first recognize the difference between amp hours and kilowatt hours. Amp hours is a measurement of electrical capacity, while kilowatt hours is a measurement of electrical power. This is just one of the many reasons why your evaluation of battery degradation is flawed.
I'm an EE and do understand the difference between amp-hours and kWh.

Amp-hours give the total number of electrons that move from one side of the battery to the other.

Watts (and kilowatts) are power.
Kilowatt-hours are energy. Our batteries are rated by kWh.

My BMS CAC value also shows 12% degradation.
 
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MY-Y

Member
Mar 4, 2020
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MD
almost surely not actual degradation and more likely your charging habits are throwing off the BMS.
That'd be great. I've tried many of the ideas on the M3 thread, including a deep cycle, sleeping for 6+ hours at many different charge levels, charging to 60, 70, 80, 85 and 90%, deep charging from 4% to 100% (once)... none of that made a lasting difference.
 
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SigNC

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Aug 23, 2017
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That'd be great. I've tried many of the ideas on the M3 thread, including a deep cycle, sleeping for 6+ hours at many different charge levels, charging to 60, 70, 80, 85 and 90%, deep charging from 4% to 100% (once)... none of that made a lasting difference.
Have you let it sit long enough to take readings at lower % as well?
 
Oct 3, 2020
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Seattle
I agree. The good news is that the reported 4% is really 8.5%. My BMS hides 3.1 kWh as an "energy buffer." I've done this only once to try to get my BMS to calibrate - it didn't change.
Be that as it may, I can assure you that lithium batteries do not like spending longer than necessary at a state of charge below 10%. This is represented by an increased rate of battery degradation.

Bottom line, the best way to hurt a lithium battery is to leave it at a very low SoC, even if only for a matter of hours.
 
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I agree. The good news is that the reported 4% is really 8.5%. My BMS hides 3.1 kWh as an "energy buffer." I've done this only once to try to get my BMS to calibrate - it didn't change.

Forgot to also mention that the energy buffer is intended to protect the empty and full states of charge, therefor there is a ‘top‘ and ‘bottom buffer.’ Some of that 3.1 kWh is for the top buffer.
 
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MY-Y

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Mar 4, 2020
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Forgot to also mention that the energy buffer is intended to protect the empty and full states of charge, therefor there is a ‘top‘ and ‘bottom buffer.’ Some of that 3.1 kWh is for the top buffer.
I didn't think that was the case. The graphical screens in scanmytesla also show it as a bottom buffer only. How did you determine it wasn't just the bottom buffer?
Screenshot_20210524-215220.jpg
 
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I didn't think that was the case. The graphical screens in scanmytesla also show it as a bottom buffer only. How did you determine it wasn't just the bottom buffer?

I‘m just clarifying that the energy buffer exists at both empty and full SoC. If you don’t specify the top or bottom buffer, I assume you’re referring to the total combined.
 
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Amp-hours give the total number of electrons that move from one side of the battery to the other.

Watts (and kilowatts) are power.
Kilowatt-hours are energy. Our batteries are rated by kWh.

I‘m an engineer as well, and this is how I would explain the difference between kWh and Ah. Kilowatt hours is a measurement of the power to do the work, while amp hours is the energy stored prior to involving any work. There is an important difference between the two, especially when trying to understand the true capacity of a battery.

As for why they’re rated in kWh, I would attribute that to the consumer and the need for there to be a universal figure to reference how big the battery is. If they were to rate them in Ah, they would also have to further complicate things by including the battery voltage.. Manufacturers would then have to rely on the consumers’ math skills when comparing to the competition.
 
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bocastephen

Member
Mar 12, 2021
16
1
Southern California
I have a standard range MY that is barely 2 months old with about 4,100 miles.

When the car was new and up to this week, maximum range was about 244 and 80% gave 219-222 of range. Those numbers held consistently regardless of when/how charged or driven.

All of a sudden and just since a) the latest software upgrade and b) getting a temporary (different) wheel due to a flat, the 80% number is now 215-216 and 100% is now 239.

I didn’t expect any degradation at this point especially as I’m careful with the battery, and this is a substantial change after this period of time and mileage, and the change is sudden, so what is the chance this is due to the software update or the temporary wheel?

I know Tesla was recently fined a significant amount for throttling range on cars in Norway through a software update.
 

SigNC

Active Member
Aug 23, 2017
1,519
1,358
NC
I have a standard range MY that is barely 2 months old with about 4,100 miles.

When the car was new and up to this week, maximum range was about 244 and 80% gave 219-222 of range. Those numbers held consistently regardless of when/how charged or driven.

All of a sudden and just since a) the latest software upgrade and b) getting a temporary (different) wheel due to a flat, the 80% number is now 215-216 and 100% is now 239.

I didn’t expect any degradation at this point especially as I’m careful with the battery, and this is a substantial change after this period of time and mileage, and the change is sudden, so what is the chance this is due to the software update or the temporary wheel?

I know Tesla was recently fined a significant amount for throttling range on cars in Norway through a software update.
This is virtually nothing and has zero to do with the 85 pack throttling.
 

MY-Y

Member
Mar 4, 2020
969
1,061
MD
I consider it something and significant if it continues degrading at this rate. I’m just trying to understand the root cause of the sudden change because I expected degredation to be slow and steady.
Look at my graph in post 9 of this thread. The BMS-reported capacity does not degrade smoothly.
 

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