How I Recovered Half of my Battery's Lost Capacity

[AlanSubie4Life]

Or am I mis-interpreting the green line?

The green line is plotted by miles, AFAIK. Not time. It’s a bit confusing. But this will largely eliminate any seasonality if it existed in the data (no idea what TeslaFi does).

 

[GtiMart]

The graph is by kilometres /miles. You can't relate that to date/temperature, we all drive different distances

 

[drtimhill]

The green line is plotted by miles, AFAIK. Not time. It’s a bit confusing. But this will largely eliminate any seasonality if it existed in the data (no idea what TeslaFi does).

ah good point.

 

[AAKEE]

The green line is plotted by miles, AFAIK. Not time. It’s a bit confusing. But this will largely eliminate any seasonality if it existed in the data (no idea what TeslaFi does).

There is year markers in teslafi, so if the driven miles is just a little spread over the year we should be able to see this.
Each point is holding date and miles so its easy to mark up the seasons etc, if needed.

Disregard the red line, its not teslafi. (Hand made aproxx of capacity in iphone).

 

[RTPEV]

Yeah, this change actually didn't change the energy you had available AFAIK. Your rated miles were just more energetic when you had 310 of them (they didn't technically change the charging constant though). The wonders of changing the degradation threshold (from ~72.5kWh to ~76kWh)! That's why it was basically rock solid at 310 (other than the initial blip which is probably bad data, or a previously unknown ability to display above ~311 when new prior to the software update increasing the range). The TeslaFi average being above 310 early on when no vehicle could exceed 310 miles was initially confusing to me, but that's because they're plotted vs. mileage, not by date, and some vehicles showed 310 miles when new, others showed 325 miles when new, so you end up with some weird average which makes no sense.

However, your car is likely slightly more efficient than when you bought it (not clear what the exact improvement was for the LR RWD).

Well, yes I do have more energy available as the software upgrade I received after I bought it gave me access to additional energy. I mean technically I did have that energy available from day 1, but what I paid for was 310 miles of range, even they they opened up more range to me later on.

 

[AlanSubie4Life]

Well, yes I do have more energy available as the software upgrade I received after I bought it gave me access to additional energy.

And what I am saying is that it is just a number, not your range. Your range increased because they changed the degradation threshold from 72.5kWh to 76kWh, while leaving the charging constant the same.

That will increase your displayed range without any change to available energy.

When you got the car, you had somewhere between 76kWh and 78kWh available. After the update you had at least 76kWh available.

Prior to the threshold change, 72.5kWh showed as 310 miles (with each mile containing at least 245Wh, but the constant was still 234Wh/mi). So your energy available was over 76kWh. (245Wh/mi*310mi = 76kWh)

Afterwards, 76kWh degradation threshold: 325miles, each mile contains at least 234Wh/mi, and the constant was left the same. So energy available was 76kWh (the same) with the range display of 325 miles.

We know the constant didn’t change because there were people who showed full range at 310 miles and then after the update did not go all the way to 325 miles. If the range update was done with a constant change then we’d have seen capacity loss before the update on these vehicles. But we didn’t. We also have energy screen pictures prior to the update, I believe. That’s how we know they used the threshold change to perform this magic. (I got this info from LR Owner a few years ago.)

But the most definitive piece of information is this: the EPA test in 2017 got 78kWh out of the LR RWD (remember, it got 334 miles in the EPA test!). It’s mandatory that manufacturers make that tested energy available to consumers - they can’t lock any out. No version of the LR RWD or LR AWD until 2021 had appreciably more than 78kWh of available energy in EPA tests; max was about 79.X kWh.

So that 78kWh was available at the time of purchase. Right now you have about 72kWh available (BMS estimate). (234Wh/mi*307mi).

Tesla just did tricky things with the range display to make the number change without changing the energy available. I know it is very confusing but that’s just how this stuff works (took a to figure out but we figured it out finally). And they likely improved the efficiency of the vehicle, improving your range.

 

[AlanSubie4Life]

Each point is holding date and miles so its easy to mark up the seasons etc, if needed.

I meant that you can see seasonality for the car in question, but cannot see seasonality for the average line. People acquire cars at different times and drive different distances each year, and the X axis is in miles, with year markers corresponding to the vehicle in question.

 

[RichardB123]

Like many others, I have been concerned with loss of 100% indicated battery range on one of my Model 3s. My P3D (build date 9/13/2018, delivery date 10/8/2018) had gotten down to 270.3 miles at 100% charge on January 20, 2020, at about 30,700 miles, which is a loss of 40.8 miles since the car was new.

I posted about going to the service center to talk with them about battery degradation, which I did on March 9, 2020. It was a great service appointment and the techs at the Houston Westchase service center paid attention to my concerns and promised to follow up with a call from the lead virtual tech team technician. I detailed this service visit in the following post:

Reduced Range - Tesla Issued a Service Bulletin for possible fix

While that service visit was great, the real meat of addressing the problem came when I spoke to the virtual tech team lead. He told me some great things about the Model 3 battery and BMS. With the knowledge of what he told me, I formulated a plan to address it myself.

So here is the deal on the Model 3 battery and why many of us might be seeing this capacity degradation.

The BMS system is not only responsible for charging and monitoring of the battery, but computing the estimated range. The way it does this is to correlate the battery's terminal voltage (and the terminal voltage of each group of parallel cells) to the capacity. The BMS tries to constantly refine and calibrate that relationship between terminal voltage and capacity to display the remaining miles.

For the BMS to execute a calibration computation, it needs data. The primary data it needs to to this is what is called the Open Circuit Voltage (OCV) of the battery and each parallel group of cells. The BMS takes these OCV readings whenever it can, and when it has enough of them, it runs a calibration computation. This lets the BMS now estimate capacity vs the battery voltage. If the BMS goes for a long time without running calibration computations, then the BMS's estimate of the battery's capacity can drift away from the battery's actual capacity. The BMS is conservative in its estimates so that people will not run out of battery before the indicator reads 0 miles, so the drift is almost always in the direction of estimated capacity < actual capacity.

So, when does the BMS take OCV readings? To take a set of OCV readings, the main HV contactor must be open, and the voltages inside the pack for every group of parallel cells must stabilize. How long does that take? Well, interestingly enough, the Model 3 takes a lot longer for the voltages to stabilize than the Model S or X. The reason is because of the battery construction. All Tesla batteries have a resistor in parallel with every parallel group of cells. The purpose of these resistors is for pack balancing. When charging to 100%, these resistors allow the low cells in the parallel group to charge more than the high cells in the group, bringing all the cells closer together in terms of their state of charge. However, the drawback to these resistors is that they are the primary cause of vampire drain.

Because Tesla wanted the Model 3 battery to be the most efficient it could be, Tesla decided to decrease the vampire drain as much as possible. One step they took to accomplish this was to increase the value of all of these resistors so that the vampire drain is minimized. The resistors in the Model 3 packs are apparently around 10x the value of the ones in the Model S/X packs. So what does this do to the BMS? Well, it makes the BMS wait a lot longer to take OCV readings, because the voltages take 10x longer to stabilize. Apparently, the voltages can stabilize enough to take OCV readings in the S/X packs within 15-20 minutes, but the Model 3 can take 3+ hours.

This means that the S/X BMS can run the calibration computations a lot easier and lot more often than the Model 3. 15-20 minutes with the contactor open is enough to get a set of OCV readings. This can happen while you're out shopping or at work, allowing the BMS to get OCV readings while the battery is at various states of charge, both high and low. This is great data for the BMS, and lets it run a good calibration fairly often.

On the Model 3, this doesn't happen. With frequent small trips, no OCV readings ever get taken because the voltage doesn't stabilize before you drive the car again. Also, many of us continuously run Sentry mode whenever we're not at home, and Sentry mode keeps the contactor engaged, thus no OCV readings can be taken no matter how long you wait. For many Model 3's, the only time OCV readings get taken is at home after a battery charge is completed, as that is the only time the car gets to open the contactor and sleep. Finally, 3 hours later, OCV readings get taken.

But that means that the OCV readings are ALWAYS at your battery charge level. If you always charge to 80%, then the only data the BMS is repeatedly collecting is 80% OCV readings. This isn't enough data to make the calibration computation accurate. So even though the readings are getting taken, and the calibration computation is being periodically run, the accuracy of the BMS never improves, and the estimated capacity vs. actual capacity continues to drift apart.

So, knowing all of this, here's what I did:

1. I made it a habit to make sure that the BMS got to take OCV readings whenever possible. I turned off Sentry mode at work so that OCV readings could be taken there. I made sure that TeslaFi was set to allow the car to sleep, because if it isn't asleep, OCV readings can't get taken.

2. I quit charging every day. Round-trip to work and back for me is about 20% of the battery's capacity, and I used to normally charge to 90%. I changed my standard charge to 80%, and then I began charging the car at night only every 3 days. So day 1 gets OCV readings at 80% (after the charge is complete), day 2 at about 60% (after 1 work trip), and day 3 at about 40% (2 work trips). I arrive back home from work with about 20% charge on that last day, and if the next day isn't Saturday, then I charge. If the next day is Saturday (I normally don't go anywhere far on Saturday), then I delay the charge for a 4th day, allowing the BMS to get OCV readings at 20%. So now my BMS is getting data from various states of charge throughout the range of the battery.

3. I periodically (once a month or so) charge to 95%, then let the car sleep for 6 hours, getting OCV readings at 95%. Don't do this at 100%, as it's not good for the battery to sit with 100% charge.

4. If I'm going to take a long drive i.e. road trip, then I charge to 100% to balance the battery, then drive. I also try to time it so that I get back home with around 10% charge, and if I can do that, then I don't charge at that time. Instead, let the car sleep 6 hours so it gets OCV readings at 10%.

These steps allowed the BMS to get many OCV readings that span the entire state of charge of the battery. This gets it good data to run an accurate calibration computation.

So what's the results?

On 1/20/2020 at 30,700 miles, I was down to 270 miles full range, which is 40.8 miles lost (15.1 %). The first good, accurate recalibration occurred 4/16/2020 at 35,600 miles and brought the full range up to 286 miles. Then another one occurred on 8/23/2020 at 41,400 miles and brought the range up to 290 miles, now only a 20 mile loss (6.9 %).

Note that to get just two accurate calibration computations by the BMS took 7 months and 11,000 miles.

So, to summarize:

1. This issue is primarily an indication/estimation problem, not real battery capacity loss.
2. Constant Sentry mode use contributes to this problem, because the car never sleeps, so no OCV readings get taken.
3. Long voltage stabilization times in the Model 3 prevent OCV readings from getting taken frequently, contributing to BMS estimation drift.
4. Constantly charging every day means that those OCV readings that do get taken are always at the same charge level, which makes the BMS calibration inaccurate.
5. Multiple accurate calibration cycles may need to happen before the BMS accuracy improves.
6. It takes a long time (a lot of OCV readings) to cause the BMS to run a calibration computation, and therefore the procedure can take months.

I would love if someone else can perform this procedure and confirm that it works for you, especially if your Model 3 is one that has a lot of apparent degradation. It will take months, but I think we can prove that this procedure will work.

This is great information.
Some are confusing battery calibration and the range estimate with degradation. This little battery symbol gives a very very crude and inaccurate estimate of battery degradation. To determine battery degradation, you need to know how many kilowatt hours your battery pack had when new, and you need to determine how many kilowatt hours still remain in that battery pack. The only perfectly accurate way would be to charge the car to 100, and then drive it down to zero. Then it can be measured. Don’t do that. You can get a pretty good estimate using Teslafi. Go on a long drive. It’s OK if you stop, because teslafi will break the trip down into segments. At the end of your trip add up the total kilowatt hours you used for each segment. Then look at the total percentage of the battery that you used. Divide the first number by the second and you have the remaining useable battery capacity in kilowatt hours. It’s got nothing to do with range, which varies widely depending on your driving habits, road conditions, temperature, tires etc. Now you have to find an accurate estimate of your total battery capacity when new. Remember there is a buffer. My 2020 model three has a buffer of 3.5 kWh.
So I would take the rated capacity when new (54 kWh) and subtract 3.5 kWh, to arrive at 50.5 available kWh when new. Using this method, My car shows minimal degradation of about 2%. Looking at the goofy little battery symbol and the mileage underneath it however, indicates almost 10% degradation. That’s not right.

 

[AlanSubie4Life]

This little battery symbol gives a very very crude and inaccurate estimate of battery degradation.

It’s actually a spectacular estimate - the best in the world for your pack, literally no one has a better estimate than the BMS - and usually quite accurate (there are exceptions, but in general it should be trusted).

My 2020 model three has a buffer of 3.5 kWh.

This is incorrect. You have a 4.5% buffer.

The only perfectly accurate way would be to charge the car to 100, and then drive it down to zero. Then it can be measured. Don’t do that.

Why not? I do it all the time on road trips. It basically matches the BMS within 1%. See the other range thread.

You can get a pretty good estimate using Teslafi. Go on a long drive. It’s OK if you stop, because teslafi will break the trip down into segments.

Better make sure TeslaFi trip segments exactly match the trip meter in the car otherwise there will be errors.

Better to use the trip meter for each segment, and log the changes in rated miles when you leave the car to when you come back to it (could go up or down).

Looking at the goofy little battery symbol and the mileage underneath it however, indicates almost 10% degradation. That’s not right.

Much more likely to be correct than the TeslaFi method. The BMS is the best estimate in the world of your pack and it is showing it right on that symbol, to within about 1% of the best known value.

 

[VT_EE]

"This is incorrect. You have a 4.5% buffer."

4.5% of a ~78kWh battery is 3.5kWh.

 

[Webeevdrivers]

4.5% of a ~78kWh battery is 3.5kWh.

I thought it was an 82 kwh battery. Or is that without the buffer.

 

[VT_EE]

I thought it was an 82 kwh battery. Or is that without the buffer.

I believe pre-2021 Model 3's were around 78kWh.

 

[AlanSubie4Life]

4.5% of a ~78kWh battery is 3.5kWh.

Note he said in his post that his car had 54kWh when new. (Unlikely to be correct; probably a 2020 SR+ with 52.5kWh or so when new - though it could possibly, though unlikely, have been as high as 54kWh.)

In any case 4.5% of that is 2.4kWh or so.

Based on his post, his car has an estimated 47.3kWh remaining, 45.1kWh usable, with a buffer of 2.2kWh.

 

[AlanSubie4Life]

I thought it was an 82 kwh battery. Or is that without the buffer.

2021 P - 80.7kWh or so, as high as 81kWh, nominally 82.1kWh
2021 AWD both 78kWh and 79kWh, depending on build date, and nominally 77.8kWh and 82.1kWh

2022 P/AWD both 82.1kWh nominally but 79kWh for the AWD and 80.7kWh or so for the P, though starting values can be higher; these are the degradation thresholds.

These values all include the buffer.

Irrelevant for this since it is an SR+ from 2020.

 

[DanDi58]

I believe pre-2021 Model 3's were around 78kWh.

The MY initially came with a 77kWh battery - mine has that (built 2/14/2021). At some point in early 2021, MYP's started shipping with the 82 kWh pack, then at some later point, it filtered out to the MYLR. As always with these changes, there is no official 'cut-over' point that can be easily identified....

 

[Rodney!]

Great thread, thank you for this!

 

[MY-Y]

The sticker under the hood of my June 2020 MY AWD said 74 kWh. Scanmytesla shows the BMS reporting 77.8 kWh. Capacity bounces between 68 and 71 kWh now.

The teslafi chart below shows that the BMS reported capacity is a wild ride. Probably best to never look at it. It just causes stress with no benefit.

 

[PCMc]

You can get a pretty good estimate using Teslafi. Go on a long drive. It’s OK if you stop, because teslafi will break the trip down into segments. At the end of your trip add up the total kilowatt hours you used for each segment. Then look at the total percentage of the battery that you used. Divide the first number by the second and you have the remaining useable battery capacity in kilowatt hours. It’s got nothing to do with range, which varies widely depending on your driving habits, road conditions, temperature, tires etc. Now you have to find an accurate estimate of your total battery capacity when new. Remember there is a buffer. My 2020 model three has a buffer of 3.5 kWh.

You may think TeslaFi is directly telling you the kWh you used, but there is nothing provided by the Tesla API (which is what TeslsFi and any app uses) to provide an actual energy usage or battery energy capacity . The only thing provided over the API is the percent SOC and the rated mile value, exactly as that displayed by the battery icon in the vehicle. If TeslaFi is reporting you an energy used term, then all they are doing is using the change in reported rated miles and converting that back into an apparent kWh energy term using a presumed rate constant for RM = kWh for the given vehicle.

So at the end of the day, any of the information you are getting from TeslaFi is built upon the exact same RM values as reported by the BMS system.

 

[AlanSubie4Life]

The teslafi chart below shows that the BMS reported capacity is a wild ride. Probably best to never look at it. It just causes stress with no benefit.

Just note it is using the rated miles directly and it is subject to large rounding error (unless you charge to 90-100% all the time) Not all of this is BMS reported capacity variation (this is not available to TeslaFi, only the projected value is).

 

[KenC]

The sticker under the hood of my June 2020 MY AWD said 74 kWh. Scanmytesla shows the BMS reporting 77.8 kWh. Capacity bounces between 68 and 71 kWh now.
View attachment 859801
The teslafi chart below shows that the BMS reported capacity is a wild ride. Probably best to never look at it. It just causes stress with no benefit.
View attachment 859803

I think the NFP is just a guesstimate by the developer. He writes about it in his blog notes.