How I Recovered Half of my Battery's Lost Capacity

[camalaio]

This part needs to be highlighted because it is precisely the opposite of what the car asks us to do.

Last month came back from a road trip with about 5% left, as soon as I press PARK the car gives me a warning to charge it ASAP to minimize the risk of going below zero. I obeyed and started charging immediately vs. letting it start at 1am as scheduled. In hindsight, I lost a good opportunity for the BMS to take a battery snapshot at 5%, plus the aforementioned cell stress avoidance.

If I may project my limited battery knowledge upon this, I found this claim a bit vague but have an idea of where it comes from.

I think the intent here is to prevent charging a hot battery at low SoC. They didn't come out and say that, but it's the only reasonable explanation I can think of. Notably, the car also won't heat the battery as much for Supercharging at low SoC (at very low SoC, it seems to be happy with just 30C, whereas it might want a 45C target for high SoC).

Traditional Li-ion charging setups disallow charging of hot batteries. Things like tools, phones, etc. all prevent charging when the battery is hot. These are devices typically charged when at low SoC only, unlike an EV which may be charged daily regardless of SoC.

If it's winter I'd say just go for it, charge right away. If it's summer, 40C (104F) outside, and your battery is likely even hotter than that, then maybe rethink it for a bit. But also internally debate how long it's actually going to take for the battery to sufficiently cool down if it's that hot.

Even better, avoid going down to 5% at all if doing so just to get "OCV readings" because of this thread (and if on hot road trips, maybe stay away from 5% if possible by adding another stop). The only point to parking at 5% is to change the BMS estimate, and the evidence for that particular theory is still largely unproven. On the other hand, there seems to be a clear suggestion that hot batteries at low SoC may not be a good idea for their health.

 

[2Old2Bold]

Have you tried voice commands? There are quite a few now.
Tap and let go; then speak after a moment or two. (old way was tap and hold).
See this list:
V10.2 Tesla Voice Commands

Thanks Scott, most helpful!

 

[Candleflame]

Thought I add something here to this post.
I just got back from a 3400km road trip (just 2 journeys of 1700km return). Car has now around 22000km.

Until 17300 km I only had 2-3% degradation being able to dump around 73kwh into a battery with a 486km max charge.
Over night my range dropped to 469km - way too quick for degradation The car gets used extensively for road trips and not much work commute so it just cycles between 65 and 50% most of the time when I go shopping and it did this for 1.5 months.

Anyway, I wanted to test a theory with teslafi and this thread whether deep cycling restores the battery just as good as leaving the car to sleep at different %. During the road trip I have done quite a few deep discharges and 100% charges and of course teslafi shows you the 100% predicted range too. I left the car shallowcycle at 60% for the month before the roadtrip to make sure the battery does not get ANY good OCV readings. (NB the reason for the frequent high charges are the huge distances here)

DATE // CHARGE TO % charge // EXTRAPOLATED 100% RANGE
27/8: 100% charge 471km
27/8 90 % charge 469km
28/8 100 % charge 469 km
28/8 70% charge 469 km
31/ 8 90% charge 469 km
31/8 95% charge 471 km
01/9 96% charge 472 km
1/9 90% charge 472 km
1/9 100% charge 473 km
2/9 94% charge 474 km

So it looks like there is a slow return of range but nothing too amazing. there were a few more charges where I didnt let it charge to a complete % so I didnt include those.

Where it gets more interesting is when you look at the extrapolated kwh which got dumped into the battery over the last few days:
I included only particularly "deep" recharges:

RECHARGE DEPTH // EXTRAPOLATED 100% CAPACITY (75kwh is no degradation w/o buffer and brick protection)

78% 72 kwh (suggests the rated range should actually be 479 rather than 469 but this was after deep cycling the battery for the first time in 1.5 months)
87% 72.5 kwh
49% 72.18 kwh
83% 72.8kwh
83% 73.6kwh

Historic charge from 2 months ago:
87% 74.33 kwh

Historic charge from April 2020 ( at 8k km)
96% 74.9kwh

Historic charge from December 2019 (at 5k km)
87% 76 kwh (this is correct, my battery started with higher than normal rated range too for the first 3 months or so, I think it was 503km or smth rather than 498km)


So it looks like the amount of kwh we can put in the battery is almost back to where it was before, bearing in mind that this is +-0.5% as teslafi does not measure decimals for initial SOC.

So it does look like driving and cycling is able to restore range as well.
I am actually going on another 2000km road trip in 8 days so we will see how high up it charges then and how much deep re-charges will get into the battery.

I have just plugged in and the estimated 100% from the app looks promising:

485 km - A few days ago this would only read 469km, sometimes 470 or 471. That said Teslas own 100% estimate tends to overestimate at low SOC so we will see...
Note that before the drop happened my rated range at 100% was 486km.

What is also important to note is that the car slept for 2 days with frequent wakeups (but resting over night) at 40% and for a few hours at 90% while on the road trip.

 

[djrodtc]

Like many others, I have been concerned with loss of 100%.....

have you tried to look what ABRP says for your battery?

https://teslamotorsclub.com/tmc/threads/abrp-battery-degradation-comparison-post-poll.197380/

 

[pigwet]

Remember to ignore data points from Stats, except the ones reported with SoC greater than 90%. All the 50% extrapolated points and lower than 90% points can be ignored. They may indicate recovery, but they can and should be aggressively ignored until you have a good datapoint at 90% charge or higher (then you can decide whether they were reasonable datapoints post hoc). Obviously there is a lot of noise on the Stats results (it's good as an estimate of capacity +/- 5-7 rated miles).

Great posts Alan. (I'm only through page 5 out of 11 now!) However, I do believe I've read that rebalancing occurs below 90% for 3's & Y's. For what it is worth, I read page 1 of these posts a bit ago as in (a) don't always charge to the same level and get some sleeps at different levels, and (b) "after a low SoC, don't charger for a few hours" comment.

For over a year I've been religiously charging to 80% with normal usage around 30 miles a day. Supercharged 4 times just for fun. Driven ~200 miles before charging maybe 20 times, charging to 90% on those days. So after one of these ~200mile days, I left it in a low state of charge for 3 hours. Then I charged to 60%, and have been charging to 60% for the last week or so. And what do I get? I'm back to fleet average. So something definitely happened at the RED dot.

 

[AlanSubie4Life]

, I do believe I've read that rebalancing occurs below 90% for 3's & Y'

Maybe so. I was just saying ignore any numbers from the Tesla App, TeslaFi, Stats below 90% SoC. Just for accuracy. Too much extrapolation error below 90% (obviously worse the lower you go...). Unrelated to rebalancing. I have no idea when rebalancing happens.

 

[hkninja]

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.

Valuable information about our Model 3, thank you. I have quite using the range estimation and rely on % of charge instead. But that makes a lot of sense and will be useful to have more accurate range estimation especially going on long trips with multiple Supercharger stops. Thanks!

 

[timk225]

Okay, here's the official answer to the OP's post #1, and a follow up to my post in entry #197. Long story short, this way of recovering miles with sentry mode off DOES NOT WORK.

Go and reread post #197, I'm too lazy to retype it all. But last night I set the charge slider to 90% and plugged the car in. I woke up this morning to 265 miles. I would have been happy with even a 269 or 270, but nope.

So after a careful week of letting the battery BMS get samples through the entire charge range, I have nothing gained. Maybe it was good in that my charging method I've been using for 2 years+ allowed it to sample the voltage all over the range to begin with, or maybe it is bad from a degradation standpoint.

Oh well, I tried.

 

[G78M3]

Okay, here's the official answer to the OP's post #1, and a follow up to my post in entry #197. Long story short, this way of recovering miles with sentry mode off DOES NOT WORK.

Go and reread post #197, I'm too lazy to retype it all. But last night I set the charge slider to 90% and plugged the car in. I woke up this morning to 265 miles. I would have been happy with even a 269 or 270, but nope.

So after a careful week of letting the battery BMS get samples through the entire charge range, I have nothing gained. Maybe it was good in that my charging method I've been using for 2 years+ allowed it to sample the voltage all over the range to begin with, or maybe it is bad from a degradation standpoint.

Oh well, I tried.

Sonewhere up thread I read that it takes several WEEKS of data points for the BMS to recalculate, i don’t think a week’s worth will do the trick

 

[TimothyHW3]

This is basically what I was saying for months and everyone was dismissing it with "If the manual says a plugged in Tesla is a happy Tesla"
No, it isn't. Especially on the Model 3 the BMS works differently than S and X

 

[SageBrush]

Sonewhere up thread I read that it takes several WEEKS of data points for the BMS to recalculate, i don’t think a week’s worth will do the trick

If not months

 

[Candleflame]

The number varies, and that's the whole basis of this discussion.

When charging batteries, the most common way is to apply higher than the cell voltage until the charging current comes to near 0A (or below a specified threshold)> You then allow the batteries to settle down (lots of chemical reactions need to complete) and measure the voltage and that becomes 100%.
If you don't charge to 100%, by watching the current go to 0, then you are only guessing.

The low voltage is measured differently, it's a combination of engineering and analysis. Basically, it is determined by the lowest voltage that nominally that doesn't cause enhanced cell damage. So while part of it comes from chemistry, real life plays in and you basically need to run a bunch of cells through testing to see what their MTBF is.

And whatever that number is, Tesla has increased it. That's how cars that set in auction houses or used car dealer lots can stay at 0 for long periods of time, because 0 really isn't 0. At a certain percent, the car starts to turn things off. And before it hits real 0%, it has turned EVERYTHING off. And, in case you didn't realize it, to measure a battery, requires the battery meter to be on, so at 0, it has to be charged, just to get the car to turn back on.

Taking the battery to 100% is a recommended practice, the manual and other places recommend it when needed.

Taking a battery to 0 isn't a great idea. I don't recommend it.

why is it a bad idea to go to 0%? Yes 0.0% is bad but from all we know 0.1% is not and cycling down to 0.1% is better than cycling up to 100%. Nevermind that Tesla has a brick protection which is likely to amount to around 2% and then the 4.5% buffer so if the car shows 0% in reality there is still 6.5% left.

 

[Candleflame]

And every one of these charts starts with an estimation/guess.

Rechargeable battery charge isn't something that can really be measured without destroying the cell. Everything else is truly an engineering estimate and, as indicated from this thread, the estimate can (and does) easily drift over time.

But yet you can create some highly detailed charts that are quite worthless.

I'm now on my 4th EV, and have learned that the battery charge is an ESTIMATE and that the battery range is an ESTIMATE.
I do know that my Model 3 with over 40,000 miles is still within 1-2 miles of initial estimates and that in real life, I'm getting about the same as initial and that I can get more than that if I want to.
And, knowing how/where I'm about to drive, be a lot more accurate than the GOM in the Model 3 or my Model Y.

well thats not true because the bms will lock the topend of the battery so even though there is some variance if your car shows 475km then the BMS has locked off the top 25km.

 

[TimothyHW3]

why is it a bad idea to go to 0%? Yes 0.0% is bad but from all we know 0.1% is not and cycling down to 0.1% is better than cycling up to 100%. Nevermind that Tesla has a brick protection which is likely to amount to around 2% and then the 4.5% buffer so if the car shows 0% in reality there is still 6.5% left.

exactly. There is bottom buffer, but no top buffer.

 

[TimothyHW3]

Okay, here's the official answer to the OP's post #1, and a follow up to my post in entry #197. Long story short, this way of recovering miles with sentry mode off DOES NOT WORK.

Sonewhere up thread I read that it takes several WEEKS of data points for the BMS to recalculate, i don’t think a week’s worth will do the trick

If not months. You have to basically drive 90% to 10% for at least 1 month to see any results.

 

[Candleflame]

exactly. There is bottom buffer, but no top buffer.

even if there is no bottom buffer - tests have shown that the issue with 0% discharges is that at 0% irreversible damage to the battery occurs due to the copper liquidifying. This is not an issue at near 0% or i.e. 0.1% - though in reality you cant guarantee that some cells might be more deplete than others so lets say for simple terms to never let it go below 1% - which is incidentially probably what brick protection does....

From the charts of batteryuniversity it seems much more healthy for the battery to cycle from i.e. 75% to 0.1% than to cycle from 100% to 25%.


Unfortunately Tesla refuses to give an official statement for this, in particular they seem to be keen to avoid range anxiety and prefer you to charge to 100%. But deep discharges come with their own advantages i.e. very quick charging.

 

[TimothyHW3]

Unfortunately Tesla refuses to give an official statement for this, in particular they seem to be keen to avoid range anxiety and prefer you to charge to 100%. But deep discharges come with their own advantages i.e. very quick charging.

I had a very strange behaviour the other day where I left the car with about 40km left on the clock and I couldn't charge it overnight so I left it and in the morning it was down to about 20km or so (didn't quite document both, but it was a large drop), which is not normal at all. I usually don't drop anything overnight and the car was asleep. Then after I charged it to 90%, limit set to 90, it overshoot and charged to 92-93% so the BMS did got crazy overnight, because I left it at 7%. So I would say going low definetely messes up the battery a bit.

 

[Candleflame]

I had a very strange behaviour the other day where I left the car with about 40km left on the clock and I couldn't charge it overnight so I left it and in the morning it was down to about 20km or so (didn't quite document both, but it was a large drop), which is not normal at all. I usually don't drop anything overnight and the car was asleep. Then after I charged it to 90%, limit set to 90, it overshoot and charged to 92-93% so the BMS did got crazy overnight, because I left it at 7%. So I would say going low definetely messes up the battery a bit.

thats normal - my car likes to do this all the time particularly if it is hot and it already did this when it was new. If i charge to 90% at a shopping centre and then drive home and let the car rest an hour later it shows 92%.

 

[TimothyHW3]

No, the temperature was the same and it was neither cold nor warm. It was ambient 20° overnight, no sun, no heat. I think it was something of a BMS mess up after it was standing overnight at low SOC. I did not document it unfortunately

 

[camalaio]

Sonewhere up thread I read that it takes several WEEKS of data points for the BMS to recalculate, i don’t think a week’s worth will do the trick

This is one of the main reasons I think the OP actually observed their pack being balanced, not some sort of calibration.

To summarize for those that don't want to read the whole thead:

• The BMS is actually very accurate. To recover that amount of range, it should not have just been the BMS being off.
• OP's changed habits allowed the car to balance much more than before, to our collective understanding of Model 3's balancing procedure.
• Imbalance can result in reduced usable pack capacity, but may be recovered if the battery simply wasn't having enough time to correct that balance.
• Recovering from imbalance is very, very slow on Model 3.

I also just can't believe that calibration would take something on the order of months. By the time you "calibrate", what have you calibrated based on? Months-old data? The pack capacity has likely gone down by then, so it requires "calibration" again, and so the cycle repeats. It just can't work that way, at least not wholly and to this degree.

well thats not true because the bms will lock the topend of the battery so even though there is some variance if your car shows 475km then the BMS has locked off the top 25km.

I'm confused by the top-end lock you're referring to, can you elaborate? (Maybe I missed something in the thread, sorry if I did)

I had a very strange behaviour the other day where I left the car with about 40km left on the clock and I couldn't charge it overnight so I left it and in the morning it was down to about 20km or so (didn't quite document both, but it was a large drop), which is not normal at all. I usually don't drop anything overnight and the car was asleep. Then after I charged it to 90%, limit set to 90, it overshoot and charged to 92-93% so the BMS did got crazy overnight, because I left it at 7%. So I would say going low definetely messes up the battery a bit.

I bet this was Sentry or Summon Standby or something, especially since you mentioned you couldn't charge it (maybe implying not being at home?). If I assume 12h overnight, that's about 240W average - implies the car was awake the whole time, as that would be about right. Or perhaps it was uploading/downloading something really slowly. Or any other reason for it to be awake. Who knows, but the numbers correspond strongly to being awake.