Battery Capacity Down to 86.8% After 18,000 Miles

[gnuarm]

I'm not sure what you mean regarding the consumption number. I believe it is well documented that the "miles" display option in the IC can vary at 100%, and I'm not sure there is anywhere else to get a "consumption number" based on the EPA rating.

Of course it will vary at 100% because 100% of what? As the capacity of the battery changes the range will vary. Mine is down about 3% from factory max. The point is the factory number doesn't vary much.

Perhaps you're saying "an ICE always has an XX gallon tank while each EV has slightly different kWh battery," but given that the batteries are all produced the same way, kWh may be the wrong measurement to think about here (perhaps each car has XX pounds of lithium or whatever, and the variance in kWh is no different but less significant than the variance between summer and winter fuel).

ICE vehicles are much more consistent in every way when it comes to mileage and range. If I buy three identical ICE cars they will be virtually identical in mileage and range and those numbers will vary only very slightly with conditions and age.

It's going to take a lot of getting used to for people to be happy with EVs and the wildly variable range and consumption. That's why I've been saying they won't become mainstream until charging is a lot more prevalent.

In either case, perhaps the closest you can come to kWh on your battery without third-party hardware or utilizing API access would be to switch to the "miles" display and do that math (at 100% charge, you would do the math against the rated distance, but at any other % charge, you would adjust the rated distance accordingly). Even then, you'd likely see variation from charge to charge and battery level to battery level. Charge to charge because cell balancing would change the reading. Battery level to battery level because the measurement isn't as simple as gallons (although arguably, one gallon of fuel could have a different amount of energy than the next and perhaps even at a different temperature).

I don't have a reason to believe those calculations. For one, when charging to 100%, the initial 5% or so comes of at a much higher consumption rate. I can tell if the regen is having an impact or not since it is not really the lack of regen, but the use of the brake that causes the lost energy. I've watched my % SoC go down much faster in the initial 5% on lower speed roads with very few uses of the brake.

I guess my use case for ICE is not typical. I literally can know my range to within 10 miles as I use the final eighth of the tank. On one occasion in the X I had to slow charge at a town because the final 50 miles or so came off at a much higher consumption rate so that I would not have reached the Supercharger. If that tiny South Carolina town had not been forward thinking enough to have a couple of level 2 chargers at the library (one wasn't working), I would have needed to knock on a door to charge somewhere.

 

[gnuarm]

This might answer the question (emphasis added).

The first wk057 quote talks about the MCU missing data on the bus during reboots. Isn't that sort of a "duh"? Not sure what it proves.

The second wk057 quote talks about the BMS getting out of calibration. If you reread my initial post you will see I did two calibration charges between <5% and 100%.

So I think your method of using the delta for the kWh from CID is probably inaccurate. A better way would be to use the rated miles reported @100% divided by the static consumption value to measure capacity/degradation.

I am still waiting on info to indicate the trip display is inaccurate. It would be very surprising to me if the trip display were as inaccurate as you say. While there can be variations in odometer readings because of tire size and inflation, everything else in the measurements should have very high precision and accuracy. I would find it surprising if there were significant errors in the numbers displayed other than energy drain not related to the drive train.

So in your case the 100% charge value indicates ~5% degradation:

RM = 277, static rated miles for 342 Wh/RM
277 miles * 342 Wh/RM = 94734 Wh
100kWh - 94.734kWh = 5.266kWh

That assumes a starting capacity of 100 kWh. I'm being told that is an assumption and likely not correct.

277/289 = 0.958, so a bit over 4% by the range.

 

[acoste]

Many here suggest the battery should be occasionally cycled between 100% charge and near 0% charge to keep the charge measurement calibrated. So I did that a couple of times. The first time the battery took a very long time to finish after it had reached 100%. It indicated around 8 kW charging rate and I switched to miles which read 276. It rose to 277 by the time the rate declined to 6 kW. The miles did not increase for another 20 or 30 minutes until it stopped charging with the rate down to 1 kW. I ran the battery down to around 3% before charging again to 100%. This time it reached 276 miles by the time it stopped charging and took a while, but not 30 minutes after reaching 100%.

There were two charges to 90% since then. I have been thinking the trip numbers were a little off, showing too small usage of kW for the percentage of the battery being used. This is a P100D, so the kW/mile should be pretty close to 1.0. I took down numbers from the trip counters. From 91% charge to 3% charge reported as 73 kW used. That's 73kWh / (91%-3%) = 83 kWh on a fully charged battery. Repeating the measurement on the trip home, a shorter distance, I get 24.3 kWh / (90%-62%) = 86.8 kWh on a full charge.

If you want to estimate the battery capacity this way, you will need to deplete the battery in one trip to make sure there is no additional charge loss regarding vampire drain. Also it is advised to drive moderately to keep the discharge current low.
This is what Tesla Bjorn does as well when measuring battery capacity.

The trip meter is not accurate for reporting kWhs, so it can't be used for degradation reporting.

It is accurate for what it does. It is based on the actual current and voltage measurements of the battery during driving. So it does not contain the battery efficiency and any losses during parking.

Because it isn't. Part of the problem is that the kWh rating of a battery is normally rated at a very low draw. The faster you take the power out the fewer kWhs you get out of it. I'm just going to make some number up here, but if you are cruising on the freeway at 50 MPH you might get 90 kWhs out of the battery, while if you are going up a hill at 70 MPH you might only get 70 kWhs out of the battery.

So the higher your Wh/mile rating the lower number of kWhs you will actually get out of the pack. (So an X will almost always get fewer kWhs out of the pack than an S will.)

That is correct. This is why consumption has to be kept low during capacity measurement. The difference is not that great though.
Battery capacity is usually rated at 0.2C
For a constant 0.2C discharge one has to drive this car at 54mph (using 100kWh battery with 92% efficiency).
To reach let's say 0.5C one has to drive at 90mph at a consumption of 510Wh/mile.

The capacity drop for the Tesla battery from 0.2C to 0.5C is around 5%.


Temperature also has some effect. For example at 20 deg C the battery has 1.5% less capacity than at 25 deg C.

That's fine if they have a tolerance, but how can they say every car has the same EPA range if the battery capacities aren't up to the stated 100 kWh?

There is certainly some variation here. First the variation within cells. (this averages out since there are many cells in the battery) and second, the build quality. There might be defective cells. Or cells whose fuse got blown.

EPA measures one specific car. It would be the car maker who could share manufacturing variation figures.

Did you ever do the same calculations when the battery was 'new'?

This. Best if one has a measurement data when the car is new and repeat the exact same measurement later. This will give a good estimation on capacity degradation.

i lose 20 miles over a 24 hour period just sitting in my garage, that's from a x75

Tesla Bjorn did some measurement on the Model 3.

With the sentry mode on he measured 300W consumtion. (7.2kWh/24h)
With sentry mode off was somewhere at 250W. (6kWh/24h)
And if I recall he added the Model X number when in deep sleep (no apps keeping the car awake), something like 50W. (1.2kWh/24h)

So I think your method of using the delta for the kWh from CID is probably inaccurate. A better way would be to use the rated miles reported @100% divided by the static consumption value to measure capacity/degradation.

Tesla occasionally reprograms the BMS which results in a different number. 2-3 years out there is a good chance that the algorithm for calculating the range is different.

Using the kWh from CID is ok as long as one uses a proper test procedure.

 

[gangzoom]

The below post suggest the energy used display doesn't report about 4kWh buffer right at the bottom end of the battery.

For me adding 4kWh to a extraprolated max 67kWh pulled from the pack on a non stop run would take me up to 71kWh just one kWh short of the reported 'usable' battery on a 75.


Calculate usable battery capacity based on rated miles values

 

[Frechtman]

I have a P100D MX HW2.0 MCU1. When I first got the vehicle, 100% charge was 285 miles max. After 10k miles, 100% charge was down to 275 miles max. Now at 20k miles, 100% charge is at 266 miles. I usually charge my MX at 90% once or twice a week and mostly using supercharger.

 

[mxnym]

I don't have a reason to believe those calculations. For one, when charging to 100%, the initial 5% or so comes of at a much higher consumption rate. I can tell if the regen is having an impact or not since it is not really the lack of regen, but the use of the brake that causes the lost energy. I've watched my % SoC go down much faster in the initial 5% on lower speed roads with very few uses of the brake.

I guess my use case for ICE is not typical. I literally can know my range to within 10 miles as I use the final eighth of the tank. On one occasion in the X I had to slow charge at a town because the final 50 miles or so came off at a much higher consumption rate so that I would not have reached the Supercharger. If that tiny South Carolina town had not been forward thinking enough to have a couple of level 2 chargers at the library (one wasn't working), I would have needed to knock on a door to charge somewhere.

I thought you wanted to know the kWh capacity on the battery. In that case, the "rated" range display option for the IC doesn't need to have anything to do with how far you can drive. If it is a calculation of <kWh on battery> x <rated miles per kWh> and the battery reading is most accurate at 100% and 0% (as roughly indicated by others in this thread) then doing the math against that number at a full charge is going to be the most accurate way to determine your battery's current capacity inside the vehicle without API/third party tools. To be clear, "that math" would be <miles displayed at full charge> / < rated miles per kWh> = <kWh capacity of battery with current cell balance>.

I agree that your use case isn't typical. Mine isn't always typical, either, so I'm very thankful that I have a 72A onboard charger, an HPWC on a 100A circuit, and a gen1 mobile charger with both 50A adapters. In my opinion, the biggest problem you have is that EV range simply isn't as high as it needs to be yet. My ICE experience includes years of a 10% difference in summer MPG vs winter MPG, but it wasn't unrealistic to get 400 miles in the summer, so 360 in the winter wasn't terrible. OTOH, in my 100D X, 295 miles in anything other than optimal conditions is unrealistic, and that's just not always enough miles, even before you start subtracting from it (obviously your P100D fares even worse and a 75D is right out for us). As such, I hope that battery technology advances lead to options to have more range than that regardless of what happens with charging infrastructure.

 

[gnuarm]

I thought you wanted to know the kWh capacity on the battery. In that case, the "rated" range display option for the IC doesn't need to have anything to do with how far you can drive. If it is a calculation of <kWh on battery> x <rated miles per kWh> and the battery reading is most accurate at 100% and 0% (as roughly indicated by others in this thread) then doing the math against that number at a full charge is going to be the most accurate way to determine your battery's current capacity inside the vehicle without API/third party tools. To be clear, "that math" would be <miles displayed at full charge> / < rated miles per kWh> = <kWh capacity of battery with current cell balance>.

My mention of the faster discharge of the battery at the high end was saying I'm not sure if I trust the numbers Tesla provides. It seems the top 5% of charge does not get you the same amount of energy as the rest.

As to using 100% and 0% to do calculations, which calculations would that be? It's not very practical to draw down to 0% as that is not good for the battery and very hard to do in practice. Starting from 100% can be done, but as has been indicated, the trip needs to be made in one go and preferably use a large percentage of the battery. Also, others have pointed out that the actual useful charge in the battery depends on the rate of withdrawing it. So knowing how many kWh your car had when it was made is not actually very useful. There are just too many variables.

Many will say, "it's the same as an ICE", but with an ICE I don't worry about predicting how far I can go on a tank. The little light comes on and I stop for gas. Done. Even when there are many more charging stations an EV won't be this simple. On a trip I will want to combine charging with a meal stop and that is a significant limitation, at least until they put chargers in more locations with decent food that isn't from Sheetz or Hardee's.

I agree that your use case isn't typical. Mine isn't always typical, either, so I'm very thankful that I have a 72A onboard charger, an HPWC on a 100A circuit, and a gen1 mobile charger with both 50A adapters. In my opinion, the biggest problem you have is that EV range simply isn't as high as it needs to be yet. My ICE experience includes years of a 10% difference in summer MPG vs winter MPG, but it wasn't unrealistic to get 400 miles in the summer, so 360 in the winter wasn't terrible. OTOH, in my 100D X, 295 miles in anything other than optimal conditions is unrealistic, and that's just not always enough miles, even before you start subtracting from it (obviously your P100D fares even worse and a 75D is right out for us). As such, I hope that battery technology advances lead to options to have more range than that regardless of what happens with charging infrastructure.

From everything I've seen the battery capacity will improve incrementally, not in large steps. Expect 20% improvement in maybe 10 years. I think they will make improvements in charging rate faster than in range. Keep in mind that EV batteries may be relatively new, but they are very much like the lithium ion technology in cell phones and laptops and they have been pushing those for some time now.

 

[acoste]

It's not very practical to draw down to 0% as that is not good for the battery and very hard to do in practice.

It isn't that scary to go down to 0%. As the hacked firmware showed there is a 4kWh buffer below 0%. And if those numbers were accurate from gangzoom's link (see the image below) the cell voltage is at 3.2V when the car shows 0%.

Some consumer electronics let the cells down to 3.0V and even to 2.8V and Panasonic says imminent damage happens below 2.5V.


So it's ok to go down to 0% occasionally. And the good thing about that is that the total capacity estimation in the BMS will remain relatively accurate so you can rely on the indication below 10% in case of a tight situation.

 

[gangzoom]

It isn't that scary to go down to 0%. As the hacked firmware showed there is a 4kWh buffer below 0%. And if those numbers were accurate from gangzoom's link (see the image below) the cell voltage is at 3.2V when the car shows 0%.

Just to confirm the screen grab on the right is the reported BMS SOC showing 5.3% versus 0% not the car display.

The cars 'energy used' display really displays some funny numbers and clearly don't capture all the energy used.

I started this trip with 100% SOC, if you do the maths based on the 'energy used' since last charge our car only has 58kWh going from 100->0%. BUT if you look at the number the range predictor is saying, the car thinks there is 23.7kWh left in the pack at 33% SOC which equates to a 100% SOC pack number of 72kWh.

Clearly there is a massive difference between the two numbers reported by the car, which tells me trying to 'guess' the absolute SOC based on BMS readings is pretty much pointless. The only real way is to charge to 100% and run the car down to 0% till it stops, than recharge back up and see what's what.

 

[Electric700]

i lose 20 miles over a 24 hour period just sitting in my garage, that's from a x75

Did you try enabling Energy Saving, with Always Connected off? Many people are seeing minimal range loss with those settings.

Many here suggest the battery should be occasionally cycled between 100% charge and near 0% charge to keep the charge measurement calibrated. So I did that a couple of times. The first time the battery took a very long time to finish after it had reached 100%. It indicated around 8 kW charging rate and I switched to miles which read 276. It rose to 277 by the time the rate declined to 6 kW. The miles did not increase for another 20 or 30 minutes until it stopped charging with the rate down to 1 kW. I ran the battery down to around 3% before charging again to 100%. This time it reached 276 miles by the time it stopped charging and took a while, but not 30 minutes after reaching 100%...

It does seem to me like a 4.2% range loss, as another member stated (277 miles / 289 original miles maximum) = 95.8% since 100% - 95.8% = 4.2%. This could be normal, and your degradation rate over time may actually decrease or stop completely, as others here have seen. I do recommend charging to 100% and then driving immediately after the charge completes once a year if possible, and don't discharge to 0% if you can avoid it. Keeping the maximum state of charge closer to 80 - 90% would be better. 50% is the ideal for li-ion batteries.

 

[gnuarm]

It isn't that scary to go down to 0%. As the hacked firmware showed there is a 4kWh buffer below 0%. And if those numbers were accurate from gangzoom's link (see the image below) the cell voltage is at 3.2V when the car shows 0%.

Some consumer electronics let the cells down to 3.0V and even to 2.8V and Panasonic says imminent damage happens below 2.5V.

So it's ok to go down to 0% occasionally. And the good thing about that is that the total capacity estimation in the BMS will remain relatively accurate so you can rely on the indication below 10% in case of a tight situation.

I seem to recall the car stops at 0% charge. What does this 4 kWh reserve do for you? In fact Bjorn had his car stop working when it showed something like 14 km left on the range. Then as he was filming the BMS and the rest of the car talked a bit more and changed it to zero. He had to have his car towed.

I don't really care what consumer batteries do. That is totally irrelevant. I need to keep my warranty intact. Tesla data shows faster degradation of the battery when charging above 90% and discharging below 10%. The nature of the battery is that the last 5% is worse than the next to last 5% and the final 1% will be the worst of all. I charge to 100% once or twice a month or if truly needed. I don't often have reason to go below 10% but will if I have little other choice. The car also has various limitations in the extreme 10% on both ends.

 

[gnuarm]

Clearly there is a massive difference between the two numbers reported by the car, which tells me trying to 'guess' the absolute SOC based on BMS readings is pretty much pointless. The only real way is to charge to 100% and run the car down to 0% till it stops, than recharge back up and see what's what.

I think I agree, but I don't think you need to run the car down to 0%. As long as you know where it started and it is reasonably low, you can do the simple math to extrapolate to 100% charge. But even that isn't the same as power drawn as someone pointed out. The real question is to find out how Tesla gauges the capacity of the battery. I'm guessing they make sure the BMS is calibrated and just ask it. That capacity should be reflected in the 100% charge range value.

 

[acoste]

I seem to recall the car stops at 0% charge. What does this 4 kWh reserve do for you? In fact Bjorn had his car stop working when it showed something like 14 km left on the range. Then as he was filming the BMS and the rest of the car talked a bit more and changed it to zero. He had to have his car towed.

Then I share gangzoom's link again. Calculate usable battery capacity based on rated miles values

The poster DB 2 drove the car until the instrument cluster showed 0%. At this point the BMS still reported 3.8kWh energy left. And 3.2V cell voltage:
"This is just after the icon changed from 1 mile to 0 miles. I reset Trip A. On the right is BMS data from TM-Spy showing 3.8 of 70.5 kWh remaining. "

Then the poster drove an additional 17 miles until BMS said it's empty, cell voltage at 3.0V
"This is after driving for 17 more miles and using 4.0 kWh. Now the BMS says I am empty. "

As long as the BMS remains accurate, the buffer exists and therefore it is ok to go down to 0%. But if one never does 100% - 0% - 100% training, the capacity estimation becomes inaccurate and may leave people stranded somewhere under the 10% territory.

Since you like to maximize the range, I suggested you keep the BMS accurate by rebalancing it occasionally. if you don't want to to it for warranty reasons, that's fine, just don't ever go below 10% then.

 

[gnuarm]

Then I share gangzoom's link again. Calculate usable battery capacity based on rated miles values

The poster DB 2 drove the car until the instrument cluster showed 0%. At this point the BMS still reported 3.8kWh energy left. And 3.2V cell voltage:
"This is just after the icon changed from 1 mile to 0 miles. I reset Trip A. On the right is BMS data from TM-Spy showing 3.8 of 70.5 kWh remaining. "

Then the poster drove an additional 17 miles until BMS said it's empty, cell voltage at 3.0V
"This is after driving for 17 more miles and using 4.0 kWh. Now the BMS says I am empty. "

As long as the BMS remains accurate, the buffer exists and therefore it is ok to go down to 0%. But if one never does 100% - 0% - 100% training, the capacity estimation becomes inaccurate and may leave people stranded somewhere under the 10% territory.

What I don't see is anything that says this "buffer" is designed in. Actually, what I see is that his battery is software limited! So he has a battery with a capacity that is actually far more than the 100% indication on the display. I don't get the point in referring to his posts.

Since you like to maximize the range, I suggested you keep the BMS accurate by rebalancing it occasionally. if you don't want to to it for warranty reasons, that's fine, just don't ever go below 10% then.

Yeah, I think I've already said I do that. I figure once a quarter is good.

 

[acoste]

What I don't see is anything that says this "buffer" is designed in. Actually, what I see is that his battery is software limited! So he has a battery with a capacity that is actually far more than the 100% indication on the display. I don't get the point in referring to his posts.

"Hughes says that the BMS indicates 98.4 kWh of usable capacity plus a 4 kWh buffer for a total of 102.4 kWh."

https://electrek.co/2017/01/24/tesla-teardown-100-kwh-battery-pack/

// Hughes is the same guy who started the thread on the previous link. In the very first post he says:

• Model X P100D: 289 rated miles * 342 Wh/mi = ~98.8 kWh usable

 

[gnuarm]

"Hughes says that the BMS indicates 98.4 kWh of usable capacity plus a 4 kWh buffer for a total of 102.4 kWh."

Teardown of new 100 kWh Tesla battery pack reveals new cooling system and 102 kWh capacity

// Hughes is the same guy who started the thread on the previous link. In the very first post he says:

• Model X P100D: 289 rated miles * 342 Wh/mi = ~98.8 kWh usable

Why does he say

The BMS reports on the full pack and may be unaware it is in a SW limited car.

What is he referring to here?

 

[acoste]

What is he referring to here?

BMS manages the battery on low level. Then it reports numbers to the car's main computer. Car computer contains the information about software limitation. BMS doesn't know it.
Car computer decides to show 0% when BMS reports 4%.
And car computer decides to show 100% when BMS reports ~80% in a software limited car.

 

[gnuarm]

BMS manages the battery on low level. Then it reports numbers to the car's main computer. Car computer contains the information about software limitation. BMS doesn't know it.
Car computer decides to show 0% when BMS reports 4%.
And car computer decides to show 100% when BMS reports ~80% in a software limited car.

Ok, so what I said is correct. When his car shows a percentage, that is not actually relevant to the real battery, but only refers to the "imaginary" battery. His posts are therefore not applicable to anyone with a full 100 kWh battery capacity on their car. Is that not correct?

 

[acoste]

Ok, so what I said is correct. When his car shows a percentage, that is not actually relevant to the real battery, but only refers to the "imaginary" battery. His posts are therefore not applicable to anyone with a full 100 kWh battery capacity on their car. Is that not correct?

I can not follow you. Bottom reserve capacity is applicable to you as well.

First guy, DK 2
What "DK 2" says is that in his software limited car
- the available capacity is 60.5kWh limited
- the BMS sees the full 70.5kWh battery
- car shows 100% when the BMS reports 86% (When fully charged, the SOC= shows 86.0% just as @wk057 reported)
- car shows 0% when the BMS reports 5.3% (3.8kWh) and the cell voltage is 3.2V
- cell voltage is 3.0V when BMS reports 0%

For you only the last 2 lines are relevant from above, but wk057 is talking about your pack specificly:

Second guy, wk057, alias jason hughes, the thread starter on the prev link
his website Pics and Info: Inside the Tesla 100kWh Battery Pack | wk057's SkieNET
- he confirmed that there is a 4kWh buffer at the bottom of the 100kWh battery

"As for real capacity, the BMS reports usable capacity at a whopping 98.4 kWh. It also reports a 4 kWh unusable bottom charge, so that's 102.4 kWh total pack capacity! Congratulations, Tesla. A high capacity pack that meets its nameplate rating!"

.

 

[Krazaak]

I seem to recall the car stops at 0% charge. What does this 4 kWh reserve do for you?

The buffer at the bottom of the battery isn't for the driver, it's for the car. At a certain point, the battery is isolated and stops providing power for any vehicle functions, including recharging the 12V battery. That buffer is well above the point where permanent damage is done to the battery and it's the reason that the car can sit for months, dead at 0% charge without being permanently bricked. It just needs to have the 12V jumped and be plugged in to charge to be brought back to life.

Driving past 0% or 0 miles is just luck that the BMS calibration is off in your favor, stopping at some low miles/km range is off to your detriment. The buffer isn't a reserve tank.