Model 3 Performance Battery Degradation One Month (Story)

[KenC]

Everything is a trade-off, between convenience, performance, range, and life. The guidelines aren't made with minimum degradation in mind, but a combination of maximum convenience and performance with acceptable degradation. For the vast majority of owners, following Tesla's guidelines is the appropriate thing to do

Alright, you’ve convinced me. I’ll do 30-80% charges for a few weeks and see how it goes. Thanks.

just one question: why isn’t this phenomenon apparent in my 2017 Model X? Charging habits are identical, and I’ve seen zero reduction in rated range in the 7 months I’ve owned it...

This is a good point, I'm wondering if the earlier-designed Model X, Tesla was more conservative. Does anyone know the top buffer size? We know the battery cells are different, the 18650s, and not the 2170s, and isn't the X battery pack actively cooled vs the 3? And isn't the chemistry also different between the S/X and the 3? So, there's lots of little things that may affect the behavior of the 3 vs the X that you own.

 

[007Bond]

OK so I got a reply about my battery range.

It looks like the Technician completed an over-the-air review of your vehicle and it will not require a visit to the service center as the findings appear to be normal. Please find his notes below for review.

• The calculated amp hour capacity of this vehicles battery does not reside in concerning bounds. No data supports the belief that the battery of this vehicle is experiencing any condition impacting it’s energy storage capacity at the time of review.

• The Mileage show on the website is based on an EPA estimate. The conditions under which this estimate was determined my not reflect the actual conditions under which this vehicle is driven.

• The Mileage calculation shown on the vehicle’s display is not an indication of HV battery capacity. It is a calculation meant to give an approximation of energy economy pertaining only to the estimated available distance of travel the vehicle is capable of at its current state of charge based on prior energy usage data.

• The vehicle’s computer only analyzes this data during charge cycles and therefore only adjusts the calculation during charge cycles. This in turn means:

1 Shorter charge cycles will allow for less data to be analyzed (less data in analyzed when charging from 80% to 90% than when charging from 40% to 90%)

2 More time between charge cycles will cause the calculation to remain unadjusted for longer periods of time and therefore be less accurate.

• All Tesla vehicles are constantly “self-checking” all of the various subsystems including the high voltage battery. Often for vehicle operationally critical subsystems (including the high voltage battery) a customer facing alert will appear on the vehicle’s display with instructions for the customer in the event the vehicle has determined a probable issue with the concerning subsystem.

• More information on battery and charging best practices can be found in the owner’s manual or at Tesla.com/support/range.



So bottom line they say nothing is wrong.

Interesting info "Shorter charge cycles will allow for less data to be analyzed" and "More time between charge cycles will cause the calculation to remain unadjusted for longer periods of time and therefore be less accurate".

So in one breath sound like they are saying keep the car plugged in all the time as more time between charge cycles leads to less accurate range estimates. BUT they also say short charge cycles analyzes less data and makes things less accurate.

So if you say charge to 90% and only drive 15 miles a short trip and you don't plan to drive the car for a few days do you plug it in or not?

Sounds like either way you are going to cause the estimate to be inaccurate.

I kinda gather that if you were to charge the car to 90% each day and drive it down below 40% each day this would lead to the most accurate range estimate after a few weeks of doing this.

 

[VT_EE]

OK so I got a reply about my battery range.

It looks like the Technician completed an over-the-air review of your vehicle and it will not require a visit to the service center as the findings appear to be normal. Please find his notes below for review.

• The calculated amp hour capacity of this vehicles battery does not reside in concerning bounds. No data supports the belief that the battery of this vehicle is experiencing any condition impacting it’s energy storage capacity at the time of review.

• The Mileage show on the website is based on an EPA estimate. The conditions under which this estimate was determined my not reflect the actual conditions under which this vehicle is driven.

• The Mileage calculation shown on the vehicle’s display is not an indication of HV battery capacity. It is a calculation meant to give an approximation of energy economy pertaining only to the estimated available distance of travel the vehicle is capable of at its current state of charge based on prior energy usage data.

• The vehicle’s computer only analyzes this data during charge cycles and therefore only adjusts the calculation during charge cycles. This in turn means:

1 Shorter charge cycles will allow for less data to be analyzed (less data in analyzed when charging from 80% to 90% than when charging from 40% to 90%)

2 More time between charge cycles will cause the calculation to remain unadjusted for longer periods of time and therefore be less accurate.

• All Tesla vehicles are constantly “self-checking” all of the various subsystems including the high voltage battery. Often for vehicle operationally critical subsystems (including the high voltage battery) a customer facing alert will appear on the vehicle’s display with instructions for the customer in the event the vehicle has determined a probable issue with the concerning subsystem.

• More information on battery and charging best practices can be found in the owner’s manual or at Tesla.com/support/range.



So bottom line they say nothing is wrong.

Interesting info "Shorter charge cycles will allow for less data to be analyzed" and "More time between charge cycles will cause the calculation to remain unadjusted for longer periods of time and therefore be less accurate".

So in one breath sound like they are saying keep the car plugged in all the time as more time between charge cycles leads to less accurate range estimates. BUT they also say short charge cycles analyzes less data and makes things less accurate.

So if you say charge to 90% and only drive 15 miles a short trip and you don't plan to drive the car for a few days do you plug it in or not?

Sounds like either way you are going to cause the estimate to be inaccurate.

I kinda gather that if you were to charge the car to 90% each day and drive it down below 40% each day this would lead to the most accurate range estimate after a few weeks of doing this.

Thanks for posting. This explanation fits in line with what everyone seems to be experiencing. Some posters have stated the consumption factor does not change. The question is then: does Tesla now lower the max range value displayed based on your driving history? It seems so.

 

[AlanSubie4Life]

what an excellent idea. Now I understand, thank you. A recent roadtrip gives these stats:


198.44 Miles Driven

251.61 Rated Miles Used

308 Wh/Mile

Battery Used
88%
61.11 kWh

Avg Speed
62 MPH

so, the constant is calculating 4.117 rated miles per kWh, or 242.87 Wh/mile.

and while that’s all well and good, all I have to do is multiply the 61.11 by 0.88 to know that my usable battery is only 69.44Kwh. So....what does this data tell you?

Just a question: It looks like this data is from TeslaFi. Can you (next time you do a similar datapoint as has been requested here) also cross check this data with the trip meter for the particular trip segment you report?

I don't use TeslaFi, so I have no idea, but I've heard that the Wh/mi data TeslaFi reports does not agree with the trip meter data in the car. Something to check - just trying to figure out why your discharge "constant" looks so high - this discrepancy would explain it (to the best of my knowledge people see 230Wh/rmi-234Wh/rmi for this "constant" for AWD vehicles - when using the trip meter data directly - it does perhaps seems to change slightly over time though that could be due to various factors). 243Wh/rmi for discharge is not a value remotely close to anything I've ever seen before (personally, or reported). It could also be caused by BMS weirdness of course.

Claim about TeslaFi Wh/mi data

If true, the way the math would work here would be:

251.61 rmi used. => 230Wh/rmi * 251.61 rmi = 57.9kWh (to 58.9kWh if using 234Wh/rmi value) used

(So actual trip meter Wh/mi would have been 57.9kWh/(198.44mi) = 292Wh/mi (or maybe as high as 297Wh/mi if using 234Wh/rmi value) - but not 308Wh/mi)

57.9kWh/0.88 = 65.8kWh full

Undegraded (per the trip meter) using 230Wh/rmi @ 310 Wh/rmi = 71.3kWh

So your battery has "degraded" to % capacity of 65.8/71.3 = 92.2%

=> 0.922*310rmi = 286 rated miles at a full charge at the time of this reading (which sounds like it aligned pretty well at the time).

So no change in the conclusions - it's really just bookkeeping about the actual constant observed on the trip meter. The perceived capacity of the battery also changes depending on what you're looking at, but the trip meter most likely doesn't align with what the BMS CAN bus read back tells you. A bit confusing.

But in the end, just curious whether the trip meter Wh/mi and TeslaFi Wh/mi actually match for a given trip.

 

[TimothyHW3]

This was actually a pretty BS copy paste reply.

Looking at your estimates it does look like in your particular case there might be just a slight battery degradation or BMS misscalibration because TeslaFi is just estimating. But in the other case with 15% off even after CAC reset, hard to tell...

But the part about:
"The Mileage calculation shown on the vehicle’s display ..."
is straight out misinformation.

What they are saying does apply to the mileage calculations when driving, but not while charging. The charging mileage is always a representation of what the BMS thinks the capacity is, because it uses basic and hard coded math:
Total capacity/typical consumption constant.

I really wish Tesla would educate their staff and drivers better...

 

[AlanSubie4Life]

Screen capture of TeslaFi and Trip Meter Discrepancy

In this case the trip meter reads HIGHER than the TeslaFi Wh/mi reports. But it sounds like there may be some randomness to it. (You can see the discharge "constant" works out to be about 235Wh/rmi for this efficient trip - though there is likely delay between the TeslaFi polling update and the trip meter, so there is some error on that calculation - may also be errors in the rated miles used reported by TeslaFi)

The summary is: TeslaFi correct data is: Miles traveled, Rated Miles Used (probably)

TeslaFi erroneous data (not matching trip meter) is: Wh/mi and kWh used

Anyway, I have no way to verify this since I don't use TeslaFi. Hopefully someone can confirm it doesn't align. But it is relevant to this discussion, when we start using "Wh/mi" and "kWh used" from TeslaFi to conclude anything. It's better to use what the car reports on the trip meter directly (and CAN bus data concurrently, if possible, of course). Ideally also just report the battery gauge miles (or better yet kilometers!) directly as accurately as possible too.

 

[gaspi101]

Just a question: It looks like this data is from TeslaFi. Can you (next time you do a similar datapoint as has been requested here) also cross check this data with the trip meter for the particular trip segment you report?

I don't use TeslaFi, so I have no idea, but I've heard that the Wh/mi data TeslaFi reports does not agree with the trip meter data in the car. Something to check - just trying to figure out why your discharge "constant" looks so high - this discrepancy would explain it (to the best of my knowledge people see 230Wh/rmi-234Wh/rmi for this "constant" for AWD vehicles - when using the trip meter data directly - it does perhaps seems to change slightly over time though that could be due to various factors). 243Wh/rmi for discharge is not a value remotely close to anything I've ever seen before (personally, or reported). It could also be caused by BMS weirdness of course.

Claim about TeslaFi Wh/mi data

If true, the way the math would work here would be:

251.61 rmi used. => 230Wh/rmi * 251.61 rmi = 57.9kWh (to 58.9kWh if using 234Wh/rmi value) used

(So actual trip meter Wh/mi would have been 57.9kWh/(198.44mi) = 292Wh/mi (or maybe as high as 297Wh/mi if using 234Wh/rmi value) - but not 308Wh/mi)

57.9kWh/0.88 = 65.8kWh full

Undegraded (per the trip meter) using 230Wh/rmi @ 310 Wh/rmi = 71.3kWh

So your battery has "degraded" to % capacity of 65.8/71.3 = 92.2%

=> 0.922*310rmi = 286 rated miles at a full charge at the time of this reading (which sounds like it aligned pretty well at the time).

So no change in the conclusions - it's really just bookkeeping about the actual constant observed on the trip meter. The perceived capacity of the battery also changes depending on what you're looking at, but the trip meter most likely doesn't align with what the BMS CAN bus read back tells you. A bit confusing.

But in the end, just curious whether the trip meter Wh/mi and TeslaFi Wh/mi actually match for a given trip.

Wow, thanks for that. the car’s trip meter often doesn’t give you an exact sum spent. It rounds off, sometimes rounding to the kWh. Tu the next time I do a longish trip I’ll take the readings. Thanks man.

 

[gaspi101]

Screen capture of TeslaFi and Trip Meter Discrepancy

In this case the trip meter reads HIGHER than the TeslaFi Wh/mi reports. But it sounds like there may be some randomness to it. (You can see the discharge "constant" works out to be about 235Wh/rmi for this efficient trip - though there is likely delay between the TeslaFi polling update and the trip meter, so there is some error on that calculation - may also be errors in the rated miles used reported by TeslaFi)

The summary is: TeslaFi correct data is: Miles traveled, Rated Miles Used (probably)

TeslaFi erroneous data (not matching trip meter) is: Wh/mi and kWh used

Anyway, I have no way to verify this since I don't use TeslaFi. Hopefully someone can confirm it doesn't align. But it is relevant to this discussion, when we start using "Wh/mi" and "kWh used" from TeslaFi to conclude anything. It's better to use what the car reports on the trip meter directly (and CAN bus data concurrently, if possible, of course). Ideally also just report the battery gauge miles (or better yet kilometers!) directly as accurately as possible too.

question: doesn’t the car’s trip meter match the data being sent out by the API? Because as I understand it, TeslaFi is doing no math. It’s just a data logger of the numbers churned out by the API.

 

[gaspi101]

OK so I got a reply about my battery range.

• The Mileage calculation shown on the vehicle’s display is not an indication of HV battery capacity. It is a calculation meant to give an approximation of energy economy pertaining only to the estimated available distance of travel the vehicle is capable of at its current state of charge based on prior energy usage data.

• The vehicle’s computer only analyzes this data during charge cycles and therefore only adjusts the calculation during charge cycles. This in turn means:

holy hell, could this really be the answer?? Am I reading this right? If the rated range is dynamic relative to driving habits (instead of a fixed EPA figure, e.g., 310 miles), then driving efficiency would affect this figure...I’m much more willing to bet I drive 15% faster/less efficiently than the EPA estimates...this also means that using rated range as a degradation yardstick is completely incorrect, and TeslaFi and Stats have incorrectly labeled their datasets (Stats got people to pay for a separate app for that, no less). Could this really be the case?

 

[gaspi101]

284.86*242.87 = 69.18kWh +-0.2%

Please share one more trip with this lower rated range when you get a chance. I wonder what's changing so wildly.

Sure thing. Here’s today’s drive:


2 Drives
Total Miles Driven 43.26
Rated Miles Used 51.32
Efficiency 84.29 %
Time Driven 1
Hours
53
Minutes
kWh Used 12.81 kWh
Wh/Mile 296 Wh
Total Cost $ 1.41
Average Temp 90.22 F

 

[FactsBot]

holy hell, could this really be the answer?? Am I reading this right? If the rated range is dynamic relative to driving habits (instead of a fixed EPA figure, e.g., 310 miles), then driving efficiency would affect this figure...I’m much more willing to bet I drive 15% faster/less efficiently than the EPA estimates...this also means that using rated range as a degradation yardstick is completely incorrect, and TeslaFi and Stats have incorrectly labeled their datasets (Stats got people to pay for a separate app for that, no less). Could this really be the case?

Tesla says this in the battery warranty section: "note that the vehicle’s range estimates are an imperfect measure of Battery capacity because they are affected by additional factors separate from Battery capacity. "

 

[FactsBot]

Sure thing. Here’s today’s drive:


2 Drives
Total Miles Driven 43.26
Rated Miles Used 51.32
Efficiency 84.29 %
Time Driven 1
Hours
53
Minutes
kWh Used 12.81 kWh
Wh/Mile 296 Wh
Total Cost $ 1.41
Average Temp 90.22 F

It should be one uninterrupted trip with constant ~65mph speed. But if I have to guess based on this data it would be 12810/51.32*270 = 67.4kWh but this is wildly inaccurate.

However one thing about the range constant: 12810/51.32 = 249.6Wh/mile
it is higher than what you had at 285 rated miles.
So when your rated range drops, the range constant goes up. So this 270 rated range is not related to battery degradation but it is some normal or erroneous behavior of the BMS software.

 

[AlanSubie4Life]

question: doesn’t the car’s trip meter match the data being sent out by the API? Because as I understand it, TeslaFi is doing no math. It’s just a data logger of the numbers churned out by the API.

I really have no idea. But you have the TeslaFi data and your trip meter so it should be pretty easy to find out!

You could imagine that they could poll data periodically and then integrate or something incorrect like that.

Anyway it seems pretty clearly wrong (based on above referenced post) sometimes, so just worth taking one of these segments you report, and report the trip meter data (which is indeed definitive - though it may not match the CAN kWh data).

It rounds off, sometimes rounding to the kWh.

As mentioned below, always report just the Wh/mi and the miles traveled. The kWh is too coarse.

 

[AlanSubie4Life]

It should be one uninterrupted trip with constant ~65mph speed. But if I have to guess based on this data it would be 12810/51.32*270 = 67.4kWh but this is wildly inaccurate.

However one thing about the range constant: 12810/51.32 = 249.6Wh/mile
it is higher than what you had at 285 rated miles.
So when your rated range drops, the range constant goes up. So this 270 rated range is not related to battery degradation but it is some normal or erroneous behavior of the BMS software.

Pretty sure the constant is off because TeslaFi is generating random data (for kWh used). But it should be easy enough to confirm/refute this.

(Of course, always report Wh/mi and miles driven, not kWh used, when reporting the trip meter, to minimize rounding error.)

 

[FactsBot]

Wow, thanks for that. the car’s trip meter often doesn’t give you an exact sum spent. It rounds off, sometimes rounding to the kWh. Tu the next time I do a longish trip I’ll take the readings. Thanks man.

This is why we multiply the miles driven by the avg consumption, that is more accurate than the rounded energy.

 

[gaspi101]

Tesla says this in the battery warranty section: "note that the vehicle’s range estimates are an imperfect measure of Battery capacity because they are affected by additional factors separate from Battery capacity. "

Yeah, but that’s talking about the energy graph, which provides these range estimates. The battery indicator is something else, is it not?

 

[FactsBot]

Yeah, but that’s talking about the energy graph, which provides these range estimates. The battery indicator is something else, is it not?

You are right, my bad. I looked up what they say about the energy display.

Energy Display:

Display remaining energy and charging units as either a percentage of battery energy remaining, or as an estimate of the distance you can drive.
Select from these options:

• Rated: Based on EPA/ECE R101 testing.
• Ideal: Assumes ideal driving conditions based on driving at a steady speed of 55 mph (89 km/h) on a flat road, and using no additional energy (seat heaters, air conditioning, etc.).
• Typical: Based on US EPA testing.

Based on this definition, it should show a number that is proportional to the battery capacity and there are no other factors involved.


That was for the Model S.
Model 3 is somewhat different:

Total estimated driving distance (or energy) available. Instead of driving distance, you can display the percentage of battery energy remaining. To do so,touch Controls > Display > Energy Display > Energy (see Controls on page95). Note: When anticipating when you need to charge, use range estimates as a general guideline only.

 

[TimothyHW3]

Yeah, but that’s talking about the energy graph, which provides these range estimates. The battery indicator is something else, is it not?

The energy graph uses your driving consumption - avg across whatever you set the past miles slider to or instant.

The battery icon uses a fixed constant which you can see in the energy graph - straight line. This value depends on the model - SR+, RWD, AWD etc.

If you match your avg(dotted line) to the typical(straight line) both energy graph estimate and battery icon will align.

But this range will still be inaccurate, because it takes you to below 0% or about -4% because of the buffer.
So
you should always subtract 4% from that estimate and then another 5-10%, whatver you want to arrive at the charger with.

So expected range in graph saying 100miles is 104%, from 100%-0 is roughly 96 miles and if you wanna end up with 10% - real est range to reach charger with 10% is 86miles

 

[AlanSubie4Life]

If you match your avg(dotted line) to the typical(straight line) both energy graph estimate and battery icon will align.

* almost...these two numerical values will align if your consumption is 5Wh/mi below the solid rated line. Very easy to verify.

 

[TimothyHW3]

* almost...these two numerical values will align if your consumption is 5Wh/mi below the solid rated line. Very easy to verify.

Yes and I have verified it - energy graph and battery estimate match at the exact line...I don't see how that could be different in miles, but it might be a display error or a rounding error. Change to km.