Battery loses SoC while parked, strange charging behavior

[dimaa_6abc]

This is anecdotal but now that I think about it, i've seen this happen as well. Usually have the charge target set to 60 or 65, and seemingly at random the car will be at 58 or 63% the next day. Plugged in the whole time.

My think is that the battery management computer has recalibrated after charging but has already sent the stop charge command. I've got a camera in the garage and even when the garage is very hot, I don't hear the car AC/Fans whatever spin up.

I also think sudden changes in SoC happen because of some recalibration. My problem is with SoC display being so inaccurate, you don't know how much range is left. Especially when it starts losing 1% per 2km vs 5km, and then 40-70% charge takes 20kWh instead of 30. So at the end this is no more than a software bug, or maybe a little bit more than software - inability to precisely estimate SoC. And considering that it starts not when the car is brand new, it might be caused by cell disbalance (just speculating).

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[Rocketair]

I also think sudden changes in SoC happen because of some recalibration. My problem is with SoC display being so inaccurate, you don't know how much range is left. Especially when it starts losing 1% per 2km vs 5km, and then 40-70% charge takes 20kWh instead of 30. So at the end this is no more than a software bug, or maybe a little bit more than software - inability to precisely estimate SoC. And considering that it starts not when the car is brand new, it might be caused by cell disbalance (just speculating).

Not disagreeing with anything you said, but after 4 years in a Taycan and following common issues, this seems to be something Porsche never had a problem with in general. So my guess is this is fundamental (or caused by a specific set of events) rather than a bug - but hope I am wrong!

 

[chrisk]

I also think sudden changes in SoC happen because of some recalibration. My problem is with SoC display being so inaccurate, you don't know how much range is left. Especially when it starts losing 1% per 2km vs 5km, and then 40-70% charge takes 20kWh instead of 30. So at the end this is no more than a software bug, or maybe a little bit more than software - inability to precisely estimate SoC. And considering that it starts not when the car is brand new, it might be caused by cell disbalance (just speculating).

Check what I did to rebalance my battery here https://www.macanevowners.com/forum/threads/very-slow-dc-charging.22212/post-333824
It solved some of the issues you described and also my very slow DC charging.
Btw if you have the Car Scanner app and an OBD2 Bluetooth dongle you can see the imbalance between the cells. Same thread as above has some related posts.

 

[dimaa_6abc]

Check what I did to rebalance my battery here https://www.macanevowners.com/forum/threads/very-slow-dc-charging.22212/post-333824
It solved some of the issues you described and also my very slow DC charging.
Btw if you have the Car Scanner app and an OBD2 Bluetooth dongle you can see the imbalance between the cells. Same thread as above has some related posts.

Thank you, I will definitely give it a try (especially because this is so simple), maybe will buy OBD2 dongle or use somebody who has one and check the disbalance before the procedure. But I must admit that I have no issues with DC fast charging. The problem caught us when we were on the long trip, and did a lot of DC fast charging on 240+ stations - no problems, max power, 200+ easily. But problem is not caused by fast charges, it began before them. Actually, the car is relatively new (less than 10 kkm), and it saw more long trips and DC fast charges than short ones and AC charges at home (3 trips 1400km one way, meaning 4200, now car has 8200, so more than half of mileage are highway trips with DC fast charges), maybe that's the cause of the disbalance.

 

[dimaa_6abc]

Thank you, I will definitely give it a try (especially because this is so simple), maybe will buy OBD2 dongle or use somebody who has one and check the disbalance before the procedure. But I must admit that I have no issues with DC fast charging. The problem caught us when we were on the long trip, and did a lot of DC fast charging on 240+ stations - no problems, max power, 200+ easily. But problem is not caused by fast charges, it began before them. Actually, the car is relatively new (less than 10 kkm), and it saw more long trips and DC fast charges than short ones and AC charges at home (3 trips 1400km one way, meaning 4200, now car has 8200, so more than half of mileage are highway trips with DC fast charges), maybe that's the cause of the disbalance.

I reread my message and see how I contradict myself. "Problem is not in DC fast charge, but car got more power from DC stations than from AC". I wanted to say that I don't have problem with DC fast charge power limit, but the car never saw DC charge with power less than 160 kW. Probably the real reason of the imbalance is too much DC fast charges.

 

[chrisk]

Thank you, I will definitely give it a try (especially because this is so simple), maybe will buy OBD2 dongle or use somebody who has one and check the disbalance before the procedure. But I must admit that I have no issues with DC fast charging. The problem caught us when we were on the long trip, and did a lot of DC fast charging on 240+ stations - no problems, max power, 200+ easily. But problem is not caused by fast charges, it began before them. Actually, the car is relatively new (less than 10 kkm), and it saw more long trips and DC fast charges than short ones and AC charges at home (3 trips 1400km one way, meaning 4200, now car has 8200, so more than half of mileage are highway trips with DC fast charges), maybe that's the cause of the disbalance.

I hope it helps. Make sure when you charge up to 90+% for the rebalancing you actually reach that SoC. My car stopped charging at 86% even though my target was 95%. I had to unplug and re-plug to continue.

 

[dimaa_6abc]

I hope it helps. Make sure when you charge up to 90+% for the rebalancing you actually reach that SoC. My car stopped charging at 86% even though my target was 95%. I had to unplug and re-plug to continue.

In the neighbor thread the owner who has similar problem (10% SoC loss in 10 days) says that some parts need to be changed, so it looks like simple rebalancing might not work.

 

[chrisk]

In the neighbor thread the owner who has similar problem (10% SoC loss in 10 days) says that some parts need to be changed, so it looks like simple rebalancing might not work.

I have seen that and I had a direct message with him. Based on what I know so far I would still try the rebalancing before I head to the dealer. It is a simple procedure and it might save you lots of headaches.

 

[Rocketair]

I have seen that and I had a direct message with him. Based on what I know so far I would still try the rebalancing before I head to the dealer. It is a simple procedure and it might save you lots of headaches.

Agreed here - as I see the similar (yet slightly different scenarios) - one that sticks out on mine is it has is a very large discrepancy on range - 80% SOC and range of 60-80 miles. If someone's is more like 200 at that SOC, it may be balancing is all that is needed.

 

[chrisk]

Agreed here - as I see the similar (yet slightly different scenarios) - one that sticks out on mine is it has is a very large discrepancy on range - 80% SOC and range of 60-80 miles. If someone's is more like 200 at that SOC, it may be balancing is all that is needed.

Both my low range estimate and losing SoC while parked were fixed after rebalancing. And DC charging speed as well. The car stopped acting weird overall.
I will now make it a habit once every thousand miles to discharge the battery to 20% and let it sit overnight then charge up and let it sit again.

 

[dimaa_6abc]

Both my low range estimate and losing SoC while parked were fixed after rebalancing. And DC charging speed as well. The car stopped acting weird overall.
I will now make it a habit once every thousand miles to discharge the battery to 20% and let it sit overnight then charge up and let it sit again.

OK, I have charged it to 90% using street AC charger and left overnight. BTW it reached 90% without stopping earlier. When I started the car next morning (it sat at least 12 hours, and it was quite cold) with the intention to drive at least 500km, it showed 91%. All the problems with sudden changes in SoC or range display were gone. Now when I charge, for example, 32%->85%, charging station says it sent 52.5kWh, while before there might be a discrepancy of 10kWh (like 41->70 charge consumed 20kWh instead of 29). Seems like low end balancing (discharge below 20% and leave overnight) is not needed anymore, but I will do it anyway, just waiting for some meaningful drives to discharge the battery. Thanks!

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