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How I Recovered Half of my Battery's Lost Capacity

Yankees

Member
May 28, 2015
191
483
Dallas
That raises another question. If someone truly believes they are headed for 30% degradation before the warranty expires, why wouldn't someone (super)charge to 100% all the time. I've never seen anything in the warranty that voids the warranty based on charging habbits. Just curious if anyone knows how Tesla handles something like that if someone "abuses" their battery leading to premature degredation? I suppose Tesla is banking on even those habits not causing serious degradation.
If I were you I'd completely not worry about it at all anymore and just do whatever felt right at the moment. Since you've lost so much range, I would charge to 100% when practical (those last few % are slow...) just so you don't get range anxiety, and then maybe check in on the battery every 3 months or so. It will either stay under 30% deg or it'll go over, but no point in sweating it really, unless you enjoy it.

A bigger problem I see is when you try to sell the car, someone savvy would check the range and be like, what is this?, sure Tesla says it's fine, but I for example would not buy such a car, because why would I? And that will be real $$$ out of your pocket. Unless you plan on keeping the car forever (or 8 years), you probably want to trade it in to a dealer when it's time for new wheels and let them deal with it.
 

Dave EV

Active Member
Jun 23, 2009
1,805
1,316
San Diego
Well that was quick. I put in a case with service indicating that my car was loosing range more quickly than others with a similar age/mileage and the desire to validate if the two TSBs for range loss for M3s around my manufacture date applied to my car. I got an nearly immediate response:

"Your vehicle doesn't qualify. The 8 year battery warranty only applies if you are loosing more than 30%. Your battery does have an 8 year warranty. At this time, there are no issues with your battery. We have closed your ticket out with us."

In other news, my car has dropped another 2 miles of displayed range down to 264 at 51,347 now (I know..I know..it may go back up). I have a couple of long trips coming up where I may try charging the battery all the way to 100% (which I have avoided ever doing up to this point) just to see if that makes any difference. To the original point of this article, I feel like I already get OCV readings at different battery charge levels because I have scheduled charging setup to start at 2AM. My car regularly sits at various battery levels (depending on what level I arrive at home with) until charging starts at 2AM already (frequently more than 6 hours of idle time). The car should have plenty of time to take readings at various levels of charge just based on my normal charging habits. The one thing I have never tried is to fully charge it to 100%. Hopefully I'll give that a shot soon before a long trip and be able to see if that has any impact. Worst case it degrades my batter a little more and gets me closer to 30% anyway.

That raises another question. If someone truly believes they are headed for 30% degradation before the warranty expires, why wouldn't someone (super)charge to 100% all the time. I've never seen anything in the warranty that voids the warranty based on charging habbits. Just curious if anyone knows how Tesla handles something like that if someone "abuses" their battery leading to premature degredation? I suppose Tesla is banking on even those habits not causing serious degradation.
It would be interesting to run ScanMyTesla on your car at various SOC levels to see what the module imbalance is at different levels.

It's too bad we can't get individual module voltages all the same time, though, like you can on older Teslas.

Knowing if it's a single module causing most of the range loss or the entire pack would be informative...
 
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rhatguy

Member
Apr 9, 2019
19
25
Atlanta GA
It would be interesting to run ScanMyTesla on your car at various SOC levels to see what the module imbalance is at different levels.

It's too bad we can't get individual module voltages all the same time, though, like you can on older Teslas.

Knowing if it's a single module causing most of the range loss or the entire pack would be informative...
i've been saving screenshots of SMT on the battery screen for a whle and I have a log of them from a few months now. Unfortunately the cell imbalance is usually near the bottom of the screen and sometimes is partially cut off. i'm mainly saving these to track my kWh loss over time, so thats what I've been making sure to capture in the screenshots. The highest imbalance I've seen has been around 8-10mV. Occasionally while charging or super charging it will go slightly higher, but it seems to settle back out. I've never seen any alarming imbalance numbers for whatever thats worth.
 

rhatguy

Member
Apr 9, 2019
19
25
Atlanta GA
I’ve heard that early owners who supercharged a lot eventually had their rates throttled a bit, so that is one reason. The other reason is that it’s expensive if you don’t have free supercharging. It’s also really inconvenient to Supercharge if you’re not road-tripping.

Just make sure it is reliably sleeping, with the contactors open. I doubt it will matter, but I guess cars that have real problems sleeping can have estimates that become fairly far off (I hear - no experience with having estimates that are wrong). Unusual and probably not the issue in your case.

At least it sounds like they confirmed that your car is not covered by the TSB (I assume that is what they meant by “your car does not qualify”).
As far as I know my car is fully sleeping when I have it parked. It is not running sentry at home, and teslamate shows it as sleeping. I also hear the contactors connect when I get ready to drive, and I don't see very high vampire drain. I think I'm good on sleep.

I don't think Tesla checked anything about the TSBs though. It was literally like 2 minutes after I submitted the service request that they came back and said it didn't "qualify". I mean I guess maybe they could have referenced the VIN quickly or checked if it was specifically flagged in their system somewhere, but I get the impression this was a "we get these every day...all Tesla's loose range...move along" type reply.
 
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AlanSubie4Life

Efficiency Obsessed Member
Oct 22, 2018
10,105
12,164
San Diego
It was literally like 2 minutes after I submitted the service request that they came back and said it didn't "qualify". I mean I guess maybe they could have referenced the VIN quickly or checked if it was specifically flagged in their system somewhere,
Reopen a service request and ask them to confirm specifically that they have done exactly this check, before they close the request. I would not even mention range loss (it doesn't matter, and is entirely unrelated to whether or not your vehicle is subject to a TSB). And for exactly that reason you mention - they hear about range loss all the time, since it is universal (and completely normal and expected!), it's best to not mention it (since it doesn't matter at all until you lose 30% anyway).

It's pretty unacceptable for them to leave things ambiguous. They definitely know which vehicles are affected and should be able to tell you: "Your vehicle is not in a VIN range affected by either of these TSBs." And then you move on.
 
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NikolaEng

New Member
Feb 22, 2021
1
0
Sequin, Wa
I'm surprised that resistors are used for cell balancing. Because voltage sensors for cells (or cell pairs) are required, it's simple to switch a resistor in to balance, if needed.
1622227834382.png

This method eliminates phantom drain. There are many other schemes to balance cells that do not require dissipating resistive heat, called active cell balancing. Some are buying Tesla batteries for home power and replacing the BMS with active cell balancing:

I have a 2021 Y that I left parked for a week. Initially, I had sentry enabled and was losing 4-5 miles/day. I disabled sentry and the phantom drain appeared to drop to zero, but the next day I lost another 4 miles. I have subscribed to TeslaFi and hope to gather more data. I just installed Scan My Tesla and hope to learn more soon. I'm a bit annoyed that Tesla does not have a specification on their website about the battery for the model Y.
 

Flybyglass

Member
Feb 2, 2020
53
57
Valencia, CA
This is good information. At 80% my estimated miles had dropped from about 252 down to 239. I have a 2/2020 AWD M3LR build and for a test I drove until the battery was at about 29%. Let it rest for about 8 hours then set it up for a scheduled charge to be ready with 80% at 6AM. I also removed temporarily my "Watch app for Tesla" (an app I really like) as it would wake the car every 15 minutes. I reset it to 5 hours but wasn't sure for this test if it would really leave the car asleep. Upon completing charge this morning estimated mileage at 80% was at 247 - a regain of 9 miles. Calculating 247/.8 = approx. 309 and my original estimated full range at 100% was 315 (I have 19's). This is not scientific but it appears to back up the idea that it's not battery degradation as much as calculation error since it takes over 3 hours for the BMS to stabilize and read and in my case most of my drives were only 10 miles before recharging and leaving plugged in. I do notice the Gen 3 chargers allow the car to drop a few miles before charging back to preset (80% in my case) where the Gen 2 chargers just held at the set limit. I am looking forward to trying this experiment again this time charging to 90% and dropping below 50% before resting and recharging.
 

ravipasupuleti

New Member
May 31, 2021
3
0
Oak Ridge, NC
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?

20200827Battery100PctRange.png


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.
Thank you. Very detailed and awesome research.
 

IChillinz

Member
Mar 19, 2021
67
61
Milwaukee, WI
My range wasnt too low at all. Was getting down to 261 when set to charge to 90%

I started setting it to charge starting at 1am so it had at least few hours or more idle time before charging when coming home. Then didnt plug it in every day if not needing. Also charging it to 100% once in while seems to help a lot. Always try to make sure and drive it shortly after getting to 100%.

This last weekend took trip to visit my parents 4 hours away so heading there and back had to charge 100%. Especially on way back made it back with out stopping to charge and probably got down to 18 miles left of range.

When I charged it I was curious what it would charge to when going back to setting it to 90%. And how its at 171-173

Was happy about that.
 

scottf200

Active Member
Feb 3, 2013
3,981
3,666
Chicagoland ModelX S603
I started setting it to charge starting at 1am so it had at least few hours or more idle time before charging when coming home.
I keep suggestion to folks to just do a scheduled departure time charge then the car will randomly start at different times (letting it have more idle time) to finish by say 6am at 80% SOC or whatever.
 

elptxjc

Member
Dec 15, 2019
828
165
El Paso, TX
I've had my M3 LR since Dec 29, so closing in on 6 months, and just passed 5K miles, most of those miles on trips, so probably about 2/3s of them on superchargers. Had to charge it once to 99%, and maybe twice to 95%, but most of the time I don't exceed 90% on trips. And at home I typically charge it when it drops to 50%, and charge it to 70%. It might take days for that to happen. The other day it dropped below 40, and supercharged it to 85 (I have free supercharging for a year).

My question is if there's any kind of 'cycle' I need to do, like supercharging to 100%, then letting it drop down to 'x' amount, or something like that, in order to minimize degradation, and/or maximize the range given on the screen? I haven't checked mileage, since I always have it in %. Thank you.
JC
 

Flybyglass

Member
Feb 2, 2020
53
57
Valencia, CA
Below is a snippet of the text conversation I had with a service advisor at my local service center. It aligns with what you were told. This text exchange was for my SR+, but I’ve been following the advice given in the text exchange below, and my new-to-me car has actually gained range since I took ownership.

View attachment 581743

View attachment 581744
There is something to this. I charged my LR Model 3 to 90% and it showed 266 miles on the EPA guess meter. Drove that day until 29% and plugged in for the night using schedule charging (scheduled start time) so it would sit for about 6 hours. The next morning right back at 90% and 266 miles. Car sat for 4 hours plugged in but not charging as the schedule to charge again was many hours from now. Checked on the charge state in the app and now is said 272 and 92%. So it was done charging but is was like the BMC's made some adjustments after 3+ hours idle and came up with new estimates of capacity state and EPA range. I had been pretty much a constant 295 miles at 100% both charging to 100% and estimated. Now the range estimate at 272 at 90% would be 302 instead of 295. If I use [email protected]% that would be back at 295. However, since the car wasn't charging there is something to the BMC's recalculating just not sure what is correct.
 

Dave EV

Active Member
Jun 23, 2009
1,805
1,316
San Diego
Something interesting I've been seeing on my car since setting up TeslaMate:

After a number of recent 15 mile freeway drives and parking at the destination, the SOC has jumped up from 2-4% 20-30 min after parking.

I wonder if this is a sign that the car is under-estimating the total capacity? I've been mostly charging to 50% the last year due to COVID and the estimated range has dropped significantly since then (I haven't been worried about it knowing that it's probably due to a miscalculation).
 

bottomsup

Member
Aug 19, 2018
191
177
ca
There is something to this. I charged my LR Model 3 to 90% and it showed 266 miles on the EPA guess meter. Drove that day until 29% and plugged in for the night using schedule charging (scheduled start time) so it would sit for about 6 hours. The next morning right back at 90% and 266 miles. Car sat for 4 hours plugged in but not charging as the schedule to charge again was many hours from now. Checked on the charge state in the app and now is said 272 and 92%. So it was done charging but is was like the BMC's made some adjustments after 3+ hours idle and came up with new estimates of capacity state and EPA range. I had been pretty much a constant 295 miles at 100% both charging to 100% and estimated. Now the range estimate at 272 at 90% would be 302 instead of 295. If I use [email protected]% that would be back at 295. However, since the car wasn't charging there is something to the BMC's recalculating just not sure what is correct.
I know the original post says to leave the car unplugged but I have been doing this method for a few months except I leave it plugged in on the day it needs to charge. The car will sit for 5-6 hours as I have it charge at midnight. I dunno what to make of it. I was down to 289 at one point, got up to 300, now I'm back to 295. Been using this method about 3 months but I don't drive a lot so charging every 5 days or so letting it run down to 20% or sometimes lower before charging to ~80 %
 

Candleflame

Active Member
Mar 9, 2015
2,964
1,381
QLD, Australia
Something interesting I've been seeing on my car since setting up TeslaMate:

After a number of recent 15 mile freeway drives and parking at the destination, the SOC has jumped up from 2-4% 20-30 min after parking.

I wonder if this is a sign that the car is under-estimating the total capacity? I've been mostly charging to 50% the last year due to COVID and the estimated range has dropped significantly since then (I haven't been worried about it knowing that it's probably due to a miscalculation).

no, thats normal. it is almost impossible to get a voltage/soc reading while the car is driving due to voltage sag. so the car just guesses.
 
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Dave EV

Active Member
Jun 23, 2009
1,805
1,316
San Diego
no, thats normal. it is almost impossible to get a voltage/soc reading while the car is driving due to voltage sag. so the car just guesses.
That is true, but the car seems to be able to measure quite accurately the amount of energy it pulls out of the pack - it has to use that to estimate SOC over time while the pack is in use.

My hypothesis is that if it thinks the pack is smaller than it really is, the SOC% will go down faster than it should until it is able to accurately estimate the resting voltage and correct.
 

Candleflame

Active Member
Mar 9, 2015
2,964
1,381
QLD, Australia
That is true, but the car seems to be able to measure quite accurately the amount of energy it pulls out of the pack - it has to use that to estimate SOC over time while the pack is in use.

My hypothesis is that if it thinks the pack is smaller than it really is, the SOC% will go down faster than it should until it is able to accurately estimate the resting voltage and correct.

it can still measure the voltage while driving its just not as accurate. and it also sees how much power is being used by the inverter.
it doesnt think the pack is smaller than it really is. it knows exactly the calibratd kwh the pack has and what the voltages are for any given SOC.
 

JonAHupp

New Member
Mar 6, 2020
2
0
Annapolis, MD
Very frustrated with my Tesla Model 3 LR (2018, delivered in 9/18). I have lost 14% of my battery capacity in under 3 years and 30,000. I'm a very careful charger, rare trips, rare supercharging, very, very rare 100% charges. Here is what I get from the service center:

IMG_0605.PNG


I don't consider 14%'slight degradation' and really don't want to have to wait another 3 years to get to 70% and a new battery. Other than the charging maneuvers outlined above, any other thoughts? Thanks. Jon
 

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