Battery cells reset/rebalancing after erratic SoC readings

[craz8]

Emptying the battery when the SOC is unreliable is a bit of an adventure. 2 miles range at 4% implies a 100% range of exactly 50 miles. The software is very confused at low charge.

On the plus side, I did just get to push my foot to the floor to make it home - I might have been able to hit 40mph if it was down hill!

Now waiting overnight to start a full charge tomorrow.

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[sor]

If it’s anything like my experience you may see the SoC increase overnight… possibly quite a bit as it unlocks stranded energy.

 

[craz8]

Indeed, it popped up to 9% and 14 miles range overnight.

Free Power!

 

[Fly4ever]

Tom you must bring down that 9% as well!!Otherwise the procedure most likely will not be correctly completed.You'll gonna see 0 miles range and 3-4% SoC.The charging session must begin when no more additional % Soc after the 12 hour "resting" period passed.You could make circles around your city block,I drove 14 Kms almost around my house trying to be safe and not left stranded in the middle of the road somewhere!Should the desirable % (4 or lower) is reached it would be safer if you stay inside your garage or near where your charger is and turn on as many power demanding features as possible.With everything turned on to maximum it took me around 20 minutes for every 1% SoC to be decreased.
Wishing you the best of luck and the best possible ourcome with the procedure!!

 

[craz8]

Too late, I’m charging now. I also don’t have time to do another 12 hour wait

Let’s see how this improves things without dropping as low as possible

 

[Fly4ever]

If your error was same as mine you should have seen a couple more % "gain" when the indicator was showing 3-4% for the second time and probably this should be the last.Anyway,when you reach the 100% unplug the car for a couple of hours and reconnect it without using the app neither the onboard feature to initiate the charge.Leave it be @100% and just reconnect the plug and initiate the charging from the charger itself.There must be additional power go into your battery.Repeat the same until no additional energy is charged.Then leave the car overnight at its "new" 100% so it will "remember/re-learn" where its upper battery limit really is.
Most likely this additional 6-7% you didn't have the time to reduce will continue to bother you even though I want to believe it will furtherly reduced even more at least a little after some charging/driving sessions.
Please post how it went!

 

[sor]

IDK if it is necessary to do the procedure twice. It probably depends on the situation. As mentioned I saw a healthy rebalance at a low of 25% SoC and full restoration of charge speed, so I’m a bit skeptical it must be driven down to nothing (and then repeated), but perhaps that’s the most thorough way.

 

[chrisk]

Too late, I’m charging now. I also don’t have time to do another 12 hour wait

Let’s see how this improves things without dropping as low as possible

You don't have to drop SoC.
I have tried with both draining and topping the battery and then leaving it undisturbed.
I have seen the battery cells rebalancing only on the top (95% in my case then leave unplugged 10hours). I have done this 3 times and I have seen it working using carscanner.

Here is an example, before rebalancing at 95%, the lowest cell voltage was 0.72v and my car would DCFC max out at 37kw

 

[craz8]

My min and max cell voltages were 0.7145 and 0.7179 at about 75% SOC. I'll check again once done to see if the delta is lowered. I never saw the slower DC charging as I almost never DC charge.

 

[craz8]

My SOC is now at 75%, and showing range of 196 miles. 2 weeks ago, 75% SOC displayed 338 miles range.

So the low end reset has certainly had an effect, and I've yet to get to the top of the SOC for that to have changed anything.

However, 65% SOC change (10-75) has been achieved with only 50kwh of power delivered, so I'm expecting that there will be some adjustment at the top end too.

 

[Fly4ever]

My SOC is now at 75%, and showing range of 196 miles. 2 weeks ago, 75% SOC displayed 338 miles range.

So the low end reset has certainly had an effect, and I've yet to get to the top of the SOC for that to have changed anything.

However, 65% SOC change (10-75) has been achieved with only 50kwh of power delivered, so I'm expecting that there will be some adjustment at the top end too.

So far it seems similar to what I get on the display for 75% SoC after my cells was rebalanced.
Since your car "thought" it received 61,75kWh instead of 50 you'll get at least another 10kWh past "100%" SoC.I would be baffled if you don't!

 

[NeilJ]

There are so many threads I could use to post my experience, however I thought it would be a way better idea to introduce a new thread regarding the SoC readings and the associated battery actual SoC (not the same thing,unfortunately,as I recently realized!)Besides,this thread will most likely provide answers and explanations to so many of us and it would be applied to so many threads in regards to the same or related issues.

As I was completely fed up with what my SoC % was keep telling me about my range and battery which were completely out of place according to what I was getting from a charger and what the car system reported I actually got,I started to suspect the SoC % was completely false for unknown reason(s).It wasn't like this right from the start but rather gradually,charge after charge and use after use the remaining power inside my battery as reported by the % SoC became more and more unrelated to the actual remaining power inside the battery.I then started to monitor how many kWh a charger was delivering for a certain charging session and how much the car "thought" it was getting: For 50% according to the SoC % there were only just 31kWh of energy delivered by the charger.Wait...50% should normally be equal to 47,5kWh,not 31!!Where were the other 16,5kWh???Was still in the battery but somehow failed to be seen and reported by the SoC system?Additionally,whatever % reported by the SoC system was actually true or there was a chance the 80% was in fact 70 or 60 or even lower??I suspected the readings were all over the place and completely unreliable so I decided to perform the so called battery cells rebalancing or SoC% reset as I called it.

I drained the battery in driving sessions in a couple of days.Every time the reported remaining SoC was going up after a couple of hours the sessions ended:while driving went down to 11%,session ended,car parked.Couple of hours later it went up to 14%. Another driving session and went to 7%,session ended,car parked.A while later went up again to 11%!!Another session around my city block this time (turtle mode and all warnings about the reduced range were on) and car parked at 4%. From then on I decided trying to reduce even more what was remaining in the battery by using only power hungry features inside the car like maximum heating everywhere inside the cabin rather than driving to avoid surprises on the road as the reported remaining Km display was now just "--" (0). Even though it reached at 2% an hour later went up again to 4% so I realized there simply wasn't an easy way to get it so low and left it at that low 4% state for 24 hours.It showed exactly the same the next day when I plugged the car in (22kWh charger) with the charging slider all the way up to 100%. Normally I should get approx.91kWh (remaining 4%=3.8kWh,95-3,8=91,2kWh) in 8 hours 40min given an avg of 10.8kW/hour charging speed.This was the exact time I was getting from the car for the charging session to be completed.I though,o.k. that's a good sign,the car "knows" it must receive another 91kWh to top up up to 100%!!!
However,at some point I started to realize that the charging session will be completed way sooner than calculated (the SoC % was constantly showing considerably higher values from what it should) in fact it ended an hour sooner!!I got exactly 80.28kWh according to the charger.Another confusion as I did the math...!!!There must be another 10-11kWh,somewhere!!!But here is the car,saying SoC 100% range 400kM!!!

When I got back to the car couple of hours later I thought:Are you absolutely certain the car has topped its battery?Was there a chance the SoC % system to not represent the actual battery SoC?It certainly was,it shows completely falls readings in the low %,how we can be sure it doesn't do the same in the high %?!!?
Disconnected the plug and plugged it once more with the reading still show 100% SoC.Guess what...:It started a new session and kept going...!!!I though to my self,naahhh...it will not get more than a couple of dozens W and the session will soon be terminated.It didn't!!!!!It kept charging another 9,8kWh ABOVE what the car was reporting as 100%!!!The new charging session lasted for almost an hour,and in fact was the hour missed from the main session earlier!!Did the math again: 3,8kWh remaining SoC + 80,28kWh main charging session + 9,8kWh secondary session = almost 94kWh.Even there was still 1kWh missing I'm sure if I would plug the car again after a while or so I'll certainly get it but doesn't mind,it won't bother me much.At least not now I know what's going on here!!Car still shows 100% now but the range went up almost another 19% to 475Km!!!

What's going on here?Definitely the SoC % system for some unknown reason(s) gradually "detach" from the actual battery SoC and start to behave erratically showing completely irrelevant readings.As the problem remain undetected therefore unsolved the readings are getting even more inaccurate,lower than the real SoC in the lows and higher in the highest actual battery SoC.Seems the gap between the actual SoC and the indicated % is getting larger below 50% and in favor of lower indicated values and vice versa above 50-60%.As we constantly charge from around 25-30 to 70-80 the issue is getting even worse and in the end no one knows at what SoC we are when we start a charging session and at what SoC we end it.Fact is the reported 80%,90% or 100% are definitely NOT REAL therefore the car never has the amount of energy displayed by the SoC% reading.

I need to underline here that I don't think all cars are having the same issue,I'm sure most of them are behaving perfectly fine.But for some reason(s)yet to be discovered some cars start to behave that way.Maybe a problematic charging session?Who knows...Thing is the issue has at least "this solution" which can be performed by us without the need to visit a service center.Certainly a service center will perform the procedure way more completely, scientifically and professionally and also without the need to have to drive our cars at a such low indicated %SoC/0Km even if we still know there's still more energy in there that the one we see!!But at least we now know the energy is there even if we've been reported otherwise.As well as that it's highly likely that in most cases we get considerably less kWh when a charging session ends than what the car tell us it got.I simply don't know yet if I do the same after a charge ending at 80% for example there will be some more kWh to get in order to reach the actual/real 80% battery as I don't know if the "trick" will also work for lower SoC other than 100%.

I also wouldn't be so surprised if the SoC 1% reduction when the car remain parked has something to do with all of this!Maybe it's only phenomenal rather than real...!After all with such SoC indication system everything seems possible!!

Please excuse my lengthy post,I wanted to analyze as much as possible the procedure and my experience as well,I believe that many fellow owners will find some answers and hopefully a likelihood solution to this issue which appears to affect quite many of us in here!!

My March 25 4S now has this problem too- so very many thanks for this solution which I’ll try over the next couple of weeks.

 

[craz8]

Continuing on! Charged to 95% - '86%' added - with only 68.5kWh provided - about 13kWh less than expected.

After the overnight BMS rebalance, I now have 85% SOC indicated, with 280 mile range, and am now topping back up to 95% for another rebalance step.

So it seems this process is both useful, and repeatable, to help get the software back on track for SOC and range.

 

[craz8]

Last evening, I charged finally to 100% and left it overnight to balance. Got in the car this morning, and it's 99% and 334 miles.

CarScanner is telling me a few things:

HV Battery Energy: 90750 Wh - Max Energy: 93650 Wh
Lowest Cell Voltage: 0.7543
Highest Cell Voltage: 0.766

So something is still not quite right, as that's quite a large voltage difference.

Also, the battery temp this morning is 70F. It hasn't been this warm for months, typically in my garage it's between 58F and 65F, so the BMS balancing was generating some heat in addition to the charging heat.

I'll do this again to 100% today after a short drive today to let the BMS do it's thing again overnight.

 

[chrisk]

Last evening, I charged finally to 100% and left it overnight to balance. Got in the car this morning, and it's 99% and 334 miles.

CarScanner is telling me a few things:

HV Battery Energy: 90750 Wh - Max Energy: 93650 Wh
Lowest Cell Voltage: 0.7543
Highest Cell Voltage: 0.766

So something is still not quite right, as that's quite a large voltage difference.

Also, the battery temp this morning is 70F. It hasn't been this warm for months, typically in my garage it's between 58F and 65F, so the BMS balancing was generating some heat in addition to the charging heat.

I'll do this again to 100% today after a short drive today to let the BMS do it's thing again overnight.

1-2% voltage difference is not bad and don't expect it to be perfect. I have seen mine being 0.01V off after rebalancing but that does not affect the DCFC speed. I had read a Taycan document that said the BMS triggers rebalancing if the inballance is more than 2%.
I also prefer to stop the charge at 95% instead of 100%, I had seen that worked better.

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