Uneven battery cell temperature when charging

[Aellseian]

I noticed a steady degradation of my SoH even though I am taking good care of the battery. 86% after 37k km/2.5 years. Only AC charging and to 70-80 percent and I live in Norway. So cold climate. What I noticed from Car Scanner is that the temperature of every third battery module is significantly hotter than the others during charging. Anyone else see the same tendency? My theory is that no matter how well I treat the battery, it is the BMS/battery itself who is treating 1/3 of the battery pack badly. Which is degrading those cells and causing the decline of SoH. I read some comments that it is a knows issue that some of the battery pouches, the way they are stacked, means some are not in direct contact with the thermal plate which has the cooling. Not sure. Anyone have any similar observation?

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[ciaranob]

First question - your profile says you're driving an Etron not a Taycan - correct? Just want to be sure we're comparing apples to apples (can't recall but am I to assume Etron's have an identical battery or is the chem different?).

But holy cow, yes your cell temps seem pretty wild albeit as you note very systematic. I have not seen this type of response at all to date - I've been tracking Soh in a separate thread for last 2+ years and many have shared cell maps but none that look like this.

May well be a BMS issue but the temp differentials seem very high to me - TBH, the only other folk with anything close to such dramatic cell temp-SoC variance usually ended up with battery replacements but not being much help here - perhaps punt a copy of this post to the Baseline Soh thread to tap into many forum experts there.

For ref you are plotting WAY off the other Cold climate cars and in fact that Soh puts your car in the Hot climate zone degradation trend (I'll add you to the graph after this post).

https://www.taycanforum.com/forum/t...ery-soh-performance.12815/page-42#post-286904

PS: If you don't mind Im adding you to the database as making you the 5th contributor from my definition of a Cold climate zone ! We have 181 Soh readings from 78 forum cars to date for all model years up to 2024 worldwide.

 

[DougFrisk]

Totally normal. There are 3 temperature sensors in each battery module. That's why you see every third one much higher. Based on my observation I think the third one in each group is the one that's closest to the bottom of the module where the heat transfer takes place. This is my car while charging. (Farenheit temps)

 

[Scandinavian]

I noticed a steady degradation of my SoH even though I am taking good care of the battery. 86% after 37k km/2.5 years. Only AC charging and to 70-80 percent and I live in Norway. So cold climate. What I noticed from Car Scanner is that the temperature of every third battery module is significantly hotter than the others during charging. Anyone else see the same tendency? My theory is that no matter how well I treat the battery, it is the BMS/battery itself who is treating 1/3 of the battery pack badly. Which is degrading those cells and causing the decline of SoH. I read some comments that it is a knows issue that some of the battery pouches, the way they are stacked, means some are not in direct contact with the thermal plate which has the cooling. Not sure. Anyone have any similar observation?

I have not got a screenshot whilst charging, but I have observed the exact same behaviour in my 2020 Turbo

The Screenshot above is when the car had done a short trip prior to charging at L2 charger. Outside temperature was below minus 5 C at the time. I wanted to see the battery temperature before plugging in.

I have looked at the temperature a number of times, but I have no screenshot of them. So this seems to be a common pattern.

 

[ciaranob]

@DougFrisk @Scandinavian

Thanks guys - again, I had never read my cell map during a charge - always after or in between and never had seen anything close to this behaviour - learning all the time and will def try to repeat this view on my next charge - any thoughts as to how quickly then the system 'balances' out in respect cell temps after a charge (as again I'm surprised if this is std. that I had not seen it before my car).

 

[Aellseian]

First question - your profile says you're driving an Etron not a Taycan - correct? Just want to be sure we're comparing apples to apples (can't recall but am I to assume Etron's have an identical battery or is the chem different?).

But holy cow, yes your cell temps seem pretty wild albeit as you note very systematic. I have not seen this type of response at all to date - I've been tracking Soh in a separate thread for last 2+ years and many have shared cell maps but none that look like this.

May well be a BMS issue but the temp differentials seem very high to me - TBH, the only other folk with anything close to such dramatic cell temp-SoC variance usually ended up with battery replacements but not being much help here - perhaps punt a copy of this post to the Baseline Soh thread to tap into many forum experts there.

For ref you are plotting WAY off the other Cold climate cars and in fact that Soh puts your car in the Hot climate zone degradation trend (I'll add you to the graph after this post).

https://www.taycanforum.com/forum/t...ery-soh-performance.12815/page-42#post-286904

PS: If you don't mind Im adding you to the database as making you the 5th contributor from my definition of a Cold climate zone ! We have 181 Soh readings from 78 forum cars to date for all model years up to 2024 worldwide.

Thanks for the reply! Its correct I have an RS etron GT, it is the same battery as far as I know. With LG Chem NCM712 E66A.
I am familiar with your chart, I’m happy to add to the statistic. Yes I am concerned about the SOH. At this rate I will be at 55% SOH after 8 years, so definitely will be a replacement.
Interesting that you haven’t seen the same trend.

@DougFrisk, @Scandinavian,
I see I was a bit quick there, indeed there are 3 lines per module. Thanks for sharing! I checked after work today, and that 3rd sensor is instantly hotter than the rest, even straight after turning on the car. Perhaps that sensor is on a circuit board or close to a lead out of the battery module that gets hotter due to the current. In another viewer in Car Scanner there is a battery min and max temp reading. I noticed that the high sensor reading is not the same as the max temp reading, it’s much lower. Would be nice to know where the sensors are placed.
Oh well, then I guess the battery simply is not strong enough to handle the high loads of the Turbo / RS Etron.

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