How I Recovered Half of my Battery's Lost Capacity

[TimothyHW3]

SageBrush said: ↑
The energy buffer grows linearly from 0 to 4.5% of nominal capacity as the RM drops from max to zero.

That is an incorrect conclusion to draw from that specific post by @TimothyHW3. The energy buffer is always 4.5% of your energy at 100%, regardless of what your SoC is. The

I think you are both wrong and correct at the same time.

The energy buffer is indeed 4.5% and stays like that with degradation (meaning at 74kWh nominal full you are at 3.3kWh and at 74.5 you are at 3.4kWh and at 77.5 you are at 3.5kWh etc.) That part is correct. But Tesla indeed hides it linearly while you drive with the different SOC%.

I show this in the video below. Basically for every 100km or 20%, Tesla hides 5km. 3.4kWh at 15.3Wh/km for the AWD LR is about 25km buffer so Tesla gradually hides those 25km by 5km increment every 100km you drive.

So at 500km the car will show you 500km. After you drive 100km at the rated constant, instead of showing you 400km left it will show you 395km left and so on.

All you need to remember is that at 100%, the shown rated range is just 96.5% of the available range from 100-0%. So if you don't want to go to about -4.5%, which you have to calculate in your head, because Tesla doesn't show negatives, you will calculate 96.5% from that 100% range and that will be your "real range" to 0%.
But you can use the total range, of course, just you will have to be carefull at 0% or below that and keep a trip meter that calculates the used kWh.

 

[TimothyHW3]

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.

No sentry doesn't work at below 20% and I don't have summon. No, my "phantom drain" is pretty good, I never get more than 1km overnight. I might have been mind-tricked or didn't remember correctly after a long drive, but I am pretty sure it wasn't that low. And going to 92% at charge limit set to 90% is something that never happened on my car, ever. It could've been some temperature thing, but the temperature was pretty stable during the night.

I think it is more a contribution to leaving the car at very low state of charge, high cell imbalance that might trick the BMS into thinking, hey - I think we might have less energy than I thought 3 hours ago. I think this is more plausible.

 

[AlanSubie4Life]

I think you are both wrong

No, I am not, it is just a different equivalent framework. It all depends on how you want to think about it I guess.

Basically for every 100km or 20%, Tesla hides 5km. 3.4kWh at 15.3Wh/km for the AWD LR is about 25km buffer so Tesla gradually hides those 25km by 5km increment every 100km you drive.

After you drive 100km at the rated constant, instead of showing you 400km left it will show you 395km left and so on.

You realize this is equivalent to a charging/discharge constant that is 4.5% less than the (correct, after correcting to 153Wh/km) EPA rated constant you are quoting right? Because the car is only actually using energy at a rate (per rated mile displayed) *lower* than the constant you are quoting.

In any case, it is entirely philosophical at this point, but I prefer to think of it as energy the car *uses* per *displayed rated* mile driven - which as you say above is DEFINITELY NOT 153Wh/km (because then it is easier to figure out how much energy it takes to charge it back up, knowing the charging efficiency is about 90% (at certain specific conditions)). Rather than thinking of energy sloshing in and out of a buffer (which is definitely not physically happening).

It’s ok to think of it your way, you just have to keep in mind the rated miles/km displayed are not the same EPA rated miles associated with the constant you are quoting. So you can’t look at the display and say I have used 100rkm, that means I have used 15.3kWh. That would be wrong.

Let’s take this discussion to another thread (the one referenced above somewhere) if you want to discuss further. While closely related, it’s a bit of a tangent from the topic at hand here.

 

[djrodtc]

I’ve stated it before but it’s probably lost in all the thread but I lost 10% of range only at 18000km.

I always charged to 80% until I tried some time ago ser always to 90% and let the charge discharge slowly using 20% per day until having 15% remaining and then charging back to 90%,
Letting the car stay put all night at about 90, 70, 50, 30 % every day I parked. I also removed sentry both at home and work and use it only in unknown places.

first time I did this “use and not charge daily” thing I charged back up to 90 at home with 16A, today I did the second time using a supercharger so si could see the degradation ABRP shows now.

I started at 448km at 100% SOC and today I’m back to 468km at 100% SOC, ABRP says I’m at 4% degradation.

In the Teslafi screenshot you can’t see the 448km because I didn’t have it yet, I started using it when charging to 90% made me recover some range that I decided to log the progress

 

[camalaio]

No sentry doesn't work at below 20% and I don't have summon. No, my "phantom drain" is pretty good, I never get more than 1km overnight. I might have been mind-tricked or didn't remember correctly after a long drive, but I am pretty sure it wasn't that low. And going to 92% at charge limit set to 90% is something that never happened on my car, ever. It could've been some temperature thing, but the temperature was pretty stable during the night.

I think it is more a contribution to leaving the car at very low state of charge, high cell imbalance that might trick the BMS into thinking, hey - I think we might have less energy than I thought 3 hours ago. I think this is more plausible.

Oh, derp, fair point. My bad. Still seems like the car was awake though with those numbers though. It could've been something like 12V battery charging (I've noticed it does this after long drives occasionally). There's so many potential explanations that all involve the car doing something for some reason, which leaves it unlikely that it's just the BMS wigging out.

I’ve stated it before but it’s probably lost in all the thread but I lost 10% of range only at 18000km.

I always charged to 80% until I tried some time ago ser always to 90% and let the charge discharge slowly using 20% per day until having 15% remaining and then charging back to 90%,
Letting the car stay put all night at about 90, 70, 50, 30 % every day I parked. I also removed sentry both at home and work and use it only in unknown places.

first time I did this “use and not charge daily” thing I charged back up to 90 at home with 16A, today I did the second time using a supercharger so si could see the degradation ABRP shows now.

I started at 448km at 100% SOC and today I’m back to 468km at 100% SOC, ABRP says I’m at 4% degradation.

In the Teslafi screenshot you can’t see the 448km because I didn’t have it yet, I started using it when charging to 90% made me recover some range that I decided to log the progress

Whoa, where in the world is ABRP getting its degradation number from? That's way off. Great, another service doing weird black-box calculations!

If you do the optimistic calculation (current 100% range divided by rated original range), that's still 6.2%, significantly higher than 4%. If you do the more honest calculation based on true kWh capacity, that puts you somewhere above 8%.

Problem is, this 100% number is coming from TeslaFi still and not the car itself. I will still caution that the 100% estimate from TeslaFi is about +-1% with you charging to 90%, and is still under many influences (the primary one being battery temperature).

Anyhow, I think you saw real increases for the same reason OP did. It's not that you were somehow giving the battery more readings probably. It's that it finally had a chance to balance, since it was never resting before due to constant Sentry Mode usage. Overall a positive result, but there was probably a quicker/easier way to get there (just charge to 80% as before, but don't use Sentry as much).

 

[timk225]

Interesting news. In my last post I had only gotten 266 miles at a 90% charge. Then I ran it down low (under 10%), and upon its 90% charge, I had 269. From that charge-up, I had run the battery part ways down during this weekend, and upon charging it to 90% again tonight, I got 271. So maybe there's some progress after all, I'll leave sentry mode off now and then at different charge levels when it can sit for at least 3 hours undisturbed, and see if it continues to improve.

 

[EvanLin]

first time I did this “use and not charge daily” thing I charged back up to 90 at home with 16A, today I did the second time using a supercharger so si could see the degradation ABRP shows now.
I started at 448km at 100% SOC and today I’m back to 468km at 100% SOC.

How many months did you do the “use and not charge daily” thing?

 

[Insilin]

I also started doing what was mentioned in the OP. Though I wasn't aware of the car having to sit 3 hours to get the full effect. Starting June 3rd I had a rated range of 458km (284 miles). Since then I've only been charging when I reach around the 20-30% range. I'm happy to report that I now see ~490km (304 miles) and it looks to be still increasing overtime.

 

[lanbo]

I also started doing what was mentioned in the OP. Though I wasn't aware of the car having to sit 3 hours to get the full effect. Starting June 3rd I had a rated range of 458km (284 miles). Since then I've only been charging when I reach around the 20-30% range. I'm happy to report that I now see ~490km (304 miles) and it looks to be still increasing overtime.

View attachment 588402

And to what SoC do you charge?

 

[Candleflame]

I believe he was referring to the discrepancy between the Tesla-measured capacity in the EPA submissions (usually measured in excess of 79kWh, to when the car stops moving, for a car with ~4000 miles on it), and the typical ~78kWh that is usually observed for a new car on the CAN bus using SMT (I am sure we have plenty of data from SMT for cars with 4000 miles and typically they will be between 77 and 78kWh I think).

The question is why there is a discrepancy there. It’s not a large difference or particularly important, but it is a curious discrepancy.

Could be scaling, could be heat losses (Tesla CAN bus capacity numbers could assume a higher average current draw than the EPA test average draw), could be a little anti-brick reserve below the buffer which can actually be used in low-draw conditions, etc. I have no idea.

In the end the starting capacity is (typically) between 78kWh and 79.5kWh, it seems. But fairly sure SMT would not ever show a number as high as 79.5kWh? Even if that is the “actual” capacity (for a given current draw).

the EPA cycle is quite gentle so they will be able to extract more power out of the cells. They also drive all cars down until they die so EPA will use the 4.5% buffer.

 

[AlanSubie4Life]

the EPA cycle is quite gentle so they will be able to extract more power out of the cells. They also drive all cars down until they die so EPA will use the 4.5% buffer.

Yes that seems quite possible. (And yes, no question the test Tesla does of the vehicle for the EPA will use all of the buffer - they drive until it stops!) Regarding gentle: I would say I have not found much difference in the rated mile constant on a freeway drive vs. around town. However, we’re just talking a 1% difference so who knows.

More to the point, it seems that the BMS (from SMT) max capacity also mismatches the EPA test. SMT seems to max out around 78kWh (I do not know what is the highest someone has seen). While the EPA test routinely ends up at 79+kWh.

So to me it looks like they use “different” kWh. But maybe they just downrate them deliberately knowing that the draw will typically be higher than it is during the EPA test.

However, speaking against that, I’ve never seen a documented extremely low draw event (even during the extreme range testing) where they seem to be able to extract more from the battery (on the trip meter) than the BMS suggests though. So that suggests there is a simple scaling issue - for what purpose, I do not know. Various speculations above.

Anyway, not a huge deal, just a very small mystery of little consequence. Certainly is not the reason why people get so confused about available energy.

 

[OverEZPZ]

Thanks for sharing your post, OP! I have a 2020 performance stealth model with 19” wheels and about 10k miles on the odometer, and I started noticing that my rated range at 100% SOC was trending down over the last few months. When my rated range hit 276 miles, I figured something was wrong with the BMS and tried everything to balance it, including charging to 100% and letting it get down to <10%, then repeating this process over the course of a couple months, which is what my service advisor (in Berkeley) recommended. None of it worked until I turned off sentry mode at home. Who knew something so simple would work? Just last night, I briefly saw 300 miles at 100% SOC while driving around town.

 

[djrodtc]

.
Whoa, where in the world is ABRP getting its degradation number from? That's way off. Great, another service doing weird black-box calculations!

If you do the optimistic calculation (current 100% range divided by rated original range), that's still 6.2%, significantly higher than 4%. If you do the more honest calculation based on true kWh capacity, that puts you somewhere above 8%.

Problem is, this 100% number is coming from TeslaFi still and not the car itself. I will still caution that the 100% estimate from TeslaFi is about +-1% with you charging to 90%, and is still under many influences (the primary one being battery temperature).

Anyhow, I think you saw real increases for the same reason OP did. It's not that you were somehow giving the battery more readings probably. It's that it finally had a chance to balance, since it was never resting before due to constant Sentry Mode usage. Overall a positive result, but there was probably a quicker/easier way to get there (just charge to 80% as before, but don't use Sentry as much).

The 100% I’m talking about is what the Tesla App estimates and what the car screen said when I charged to 100% and that has always be the same as what TeslaFi says, that, at least I know I can trust.

Anyhow, like you said I’m planning to stay at 90 for a while and the try going back to 80 but this time I will monitorize the range

 

[djrodtc]

How many months did you do the “use and not charge daily” thing?

I did one week 90-15-90 once per week, I did one or two weeks 90-70-90 daily, then I went on vacation for another week and then the car stayed plugged in at 90%, then this week 90-15-90 once a week again and that’s it, I’m back to 90-70-90 daily now

 

[djrodtc]

I also started doing what was mentioned in the OP. Though I wasn't aware of the car having to sit 3 hours to get the full effect. Starting June 3rd I had a rated range of 458km (284 miles). Since then I've only been charging when I reach around the 20-30% range. I'm happy to report that I now see ~490km (304 miles) and it looks to be still increasing overtime.

View attachment 588402

Wow!!! Your case mimics mine, maybe I should continue charging when I’m low and not everyday and see what happens.
What is your sentry mode use?

 

[camalaio]

The 100% I’m talking about is what the Tesla App estimates and what the car screen said when I charged to 100% and that has always be the same as what TeslaFi says, that, at least I know I can trust.

Anyhow, like you said I’m planning to stay at 90 for a while and the try going back to 80 but this time I will monitorize the range

Actually, I would advise not trusting the in-app number. It is deriving it the same way as TeslaFi (as you noticed), and it absolutely can be quite wrong. I've outlined in previous posts that it reported 476km (I think?) while the actual range at 100% was closer to 482km for me (I'd have to find that post again to be sure).

Anyways, point is that app estimate is misleading in the exact same way as TeslaFi. Technically this isn't surprising since they use the exact same data, but it is a little bit disappointing.

 

[toolman335]

Thanks for sharing your post, OP! I have a 2020 performance stealth model with 19” wheels and about 10k miles on the odometer, and I started noticing that my rated range at 100% SOC was trending down over the last few months. When my rated range hit 276 miles, I figured something was wrong with the BMS and tried everything to balance it, including charging to 100% and letting it get down to <10%, then repeating this process over the course of a couple months, which is what my service advisor (in Berkeley) recommended. None of it worked until I turned off sentry mode at home. Who knew something so simple would work? Just last night, I briefly saw 300 miles at 100% SOC while driving around town.

View attachment 588817

This^^^^^^
I'm definitely noticing a TMC trend that maybe, just maybe, once in a while the car wants to be left alone. Everyone is obsessed with monitoring every aspect of these cars. We have to always have Sentry mode on, have it plugged in 24/7, and monitor 1,000 data points about the battery from half a dozen third party apps.

My range has remained excellent since I bought it. I don't think about the range or battery health at all. My car gets completely uninterrupted sleep for 10 hours at work and 10 hours every night. I honestly can't recall the last time I opened the App on my phone(I don't use Sentry mode). Maybe she just wants some peace? Try it and see if that works!

 

[jlindy]

Maybe a dumb question here but the first time I noticed a drop in stated range was after I left my car plugged in over night. I had previously, and ever since seeing that drop, Removed the charging cable once the charge is complete. I know the car is doing calculations unplugged at various states of charge as long as sentry mode is off but after you charge it back up does it also do calculations after that IF it is still plugged in until the next morning? Alternatively should I still unplug after it charges so it can fully go to sleep or will it sleep plugged in too?

 

[Zoomit]

Maybe a dumb question here but the first time I noticed a drop in stated range was after I left my car plugged in over night. I had previously, and ever since seeing that drop, Removed the charging cable once the charge is complete. I know the car is doing calculations unplugged at various states of charge as long as sentry mode is off but after you charge it back up does it also do calculations after that IF it is still plugged in until the next morning? Alternatively should I still unplug after it charges so it can fully go to sleep or will it sleep plugged in too?

Generally, whether the car is plugged in or not has no influence on the BMS calibration, nor does it influence if your car sleeps or not. It will influence when it wakes up occasionally though. When plugged in and under long-term storage, my car will wake at 10pm, my normal charge start time. When unplugged, it wakes at midnight. I suspect this is just a “phone home” check. This is based on TeslaFi and OpenEVSE data logging.

Many people think the car uses their EVSE more than it actually does. Over the 2 years I’ve owned it, I have NEVER seen my car pull power from the wall other than planned charging; top-up charging during storage; HVAC use for set preconditioning, deliberate preconditioning, or an open door; or if I’m just in the car fiddling with it. I expect if my garage was super hot or super cold it would pull power for battery temp control, but I have never seen it. The annual temperature range for my garage is about 20 F to 90 F.

So in summary, leave it plugged in and don’t worry about it.

 

[Dave EV]

So in summary, leave it plugged in and don’t worry about it.

Or don't leave it plugged in, and don't worry about it, either.

Unless you're going to leave it unplugged for months, then you probably want to leave it plugged in and set to 50%.