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How I Recovered Half of my Battery's Lost Capacity

This guy hits the mail on the head. Drive your car's battery down. Recharge to 80/85/90 percent. DO NOT charge every day and DO NOT charge right after driving. Let the car rest. I was recently getting 197-199 miles @ 90% (M3SRP 240 miles @ 100% 216 @ 90%). This morning I got it up to 205 miles.
THIS WORKS
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.





This guy hits the mail on the head. Drive your car's battery down. Recharge to 80/85/90 percent. DO NOT charge every day and DO NOT charge right after driving. Let the car rest. I was recently getting 197-199 miles @ 90% (M3SRP 240 miles @ 100% 216 @ 90%). This morning I got it up to 205 miles.
THIS WORKS
 
So, what happened here - where did I just lose 2kWh in about a month and a half?

Model 3P, 06/2021, 21k km (13k miles). I have been charging to 80%/90% regularly and the trend in TeslaFi looks OK. Then about couple of months back I changed the routine a bit and wanted to try out the method in this thread. Not necessarily charging every day and giving the battery measurements from different percentages and letting the car sleep (6-8h) and then charging. The only other thing changed is the weather which now is quite a bit warmer here in Finland.

Now my range is down from ~487km to 473km (303miles to 294 miles) so lost 15km (~+9 miles). ScanMyTesla also shows a 2kWh drop, from 77.4 kWh to 75.4 kWh. TeslaFi used to show way above average and now I am way down. (I did a 100% charge to check)

Any advice?
Thanks!

teslafi.jpg
tesla_SMT.PNG
 

N54TT

Active Member
Aug 14, 2018
1,047
891
NY
Any advice?
Thanks!

Unless you’re getting to the point of where you’re looking to warranty the battery…..Charge to whatever you want and just enjoy the car.

Tesla won’t do anything until you get to that 30% degradation. I’ve been charging my performance August 2018 build with 51k miles to 90% daily since I took delivery. My displayed range at 100% dropped from as low as [email protected] back up to 288 at 46k, with no change in charging habits. Even at a displayed range of 265 at 100% it didn’t effect my daily driving habits nor my longer road trips. I was still stopping at the same chargers I did when it was brand new. My daily driving is only about 45-50 miles/day. Why do I charge to 90% every day? Because I don’t enjoy the lack of power at lower SOC’s And the reason I bought the car was for that power. FWI I’ve been there done that….bought a BT dongle and wire harness to use SMT with my iPhone. While I do still track my ranges at end of charge….I’ve resorted to the set it and forget mentality and stopped worrying where my miles went.
 

MY-Y

Active Member
Mar 4, 2020
1,374
1,655
MD
I posted something in the MY forum to help with degradation anxiety. I hope it helps.
 
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So, what happened here - where did I just lose 2kWh in about a month and a half?

Model 3P, 06/2021, 21k km (13k miles). I have been charging to 80%/90% regularly and the trend in TeslaFi looks OK.

Now my range is down from ~487km to 473km (303miles to 294 miles) so lost 15km (~+9 miles). ScanMyTesla also shows a 2kWh drop, from 77.4 kWh to 75.4 kWh. TeslaFi used to show way above average and now I am way down. (I did a 100% charge to check)

Any advice?
Thanks!
Using 80-90% regularly and letting the car stand long times with high SOC will degrade your battery faster(than lower SOC).
I you havent seen my posts earlier about how to reduce degradation you could read some of them(search for my nick and for xample [calendar aging].
Your battery wont break as you use it right now but you probably cause more than twice the degradation compared to a battery conservative approach. You do not seem to need touse 80-90% daily? As you ask about degradation and range/NFP it seems like you care aboutthe degradation…

My ’21 M3P is soon 1 1/2 years, 42.000km and I just got below 500km in range.
NFP is about 79kWh. I have quite some full charges and about 17-20% supercharging, still very low degradation.
Actually I had full range until recently when I did a inverted 4G negative di….just kidding, I did a inverted BMS calibratioj to see the true capacity. I have had around 80.5-81 kWh NFP since forever.
 

Fiver

Active Member
Apr 10, 2015
1,991
1,781
Utah
Unless you’re getting to the point of where you’re looking to warranty the battery…..Charge to whatever you want and just enjoy the car.

Tesla won’t do anything until you get to that 30% degradation. I’ve been charging my performance August 2018 build with 51k miles to 90% daily since I took delivery. My displayed range at 100% dropped from as low as [email protected] back up to 288 at 46k, with no change in charging habits. Even at a displayed range of 265 at 100% it didn’t effect my daily driving habits nor my longer road trips. I was still stopping at the same chargers I did when it was brand new. My daily driving is only about 45-50 miles/day. Why do I charge to 90% every day? Because I don’t enjoy the lack of power at lower SOC’s And the reason I bought the car was for that power. FWI I’ve been there done that….bought a BT dongle and wire harness to use SMT with my iPhone. While I do still track my ranges at end of charge….I’ve resorted to the set it and forget mentality and stopped worrying where my miles went.
I wrote a much more snarky post, but after reflection I'm going to just boil it down to this: Not everyone has the same ownership experience in regards to their battery capacity. What "works" for one might not work for others. There are hundreds of thousands of Teslas out there now, and while mostly similar, there are bound to be differences in packs just given the sheer numbers. I'm glad your experience has been positive, but be understanding of others who might not be having such smooth sailing.
 
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N54TT

Active Member
Aug 14, 2018
1,047
891
NY
I wrote a much more snarky post, but after reflection I'm going to just boil it down to this: Not everyone has the same ownership experience in regards to their battery capacity. What "works" for one might not work for others. There are hundreds of thousands of Teslas out there now, and while mostly similar, there are bound to be differences in packs just given the sheer numbers. I'm glad your experience has been positive, but be understanding of others who might not be having such smooth sailing.

My latest Tesla experience has been less than ideal. Had to get my car towed last week at 51k( just out of warranty), needs a part that isn‘t in stock nationwide, have no eta on repair and Service center communication is lackluster.

In regards to capacity loss……where was I not understanding? People will certainly have differences in packs. I have been using 18650 cells in led flashlights for years before I got my Tesla and know there are differences in cells let alone whole battery packs. Owners can worry/stress about how to care for the battery, recover lost capacity etc. But most people don’t have unbalanced packs…more likely variances in pack capacity. There’s been numerous posts about people attempting to recover lost capacity with zero effect, as well as situations like myself that have experienced variances without doing anything. IMO there’s too many people worrying about where their 10miles of range went and go out of their way to try and recover it. There should be more public awareness of the possible variances in capacity and how it can/will fluctuate throughout ownership. In the end, FACT is there will be variances in packs and Tesla wont do anything until an owner hits the 30% loss. I stand by just set it to what you want, forget it and enjoy the car….until you get closer to that 30% loss.

I see you‘ve been a long time owner. I don’t know about the new LFP packs….but It seems the 18650 cells in the s/x see less variability during ownership than the 2170’s in the 3/Y as well as initial degradation is greater in the 3/y than it has been in the S/X.
 
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N54TT

Active Member
Aug 14, 2018
1,047
891
NY
I wrote a much more snarky post, but after reflection I'm going to just boil it down to this: Not everyone has the same ownership experience in regards to their battery capacity. What "works" for one might not work for others. There are hundreds of thousands of Teslas out there now, and while mostly similar, there are bound to be differences in packs just given the sheer numbers. I'm glad your experience has been positive, but be understanding of others who might not be having such smooth sailing.

Just got my car back after 3 weeks in service…. had the high voltage controller and power conversion system replaced. My latest charge this morning to 90% was 246…figure [email protected]%. So be it…..will just keep doing what I’ve been doing, keep notice of my end of charge and go back to Tesla when my 90% end of charge gets closer to 200. August 2018 build, performance 3, 51k miles, and lifetime avg 321wh/mile.
 

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