85 kWh refurb +100mV imbalance

[rns-e]

One of my friends is experiencing a few HV battery issues. The battery is still under warranty, but Tesla says the battery is fine.

When the shows around 10-12% SoC it will just die, no power what so ever. This has happened to him a few times on vacation a 1.000 Km from home. It will not charge to 100% and the typical at maximum charge is now showing around 320 Km.

We've had the Scan my Tesla connected and it shows that module 2 is +100mV off balance with the other modules.

It is a refurb battery and it came somewhat imbalanced almost two years ago and he has repeatedly been told that it will balance it self, but the imbalance has just gotten worse and worse and culminated this summer by shutting down abruptly while saying it had 60 Km left.

So anybody have any idea what to do?

 

[danielk04]

Interesting!
You are the first person I've known to validate Jason Hugh's battery findings.
My guess is that Tesla changed one or more modules in your replacement high voltage pack and the slight specification mismatch in all the individual bricks cannot be corrected by the small BMS bleeder current and instead move further apart in voltage over time, resulting in a premature "dead" battery at 10% indicated, and premature "charge complete" at the top end.
Now, can you get this across to your local Tesla service center? An uphill battle.
Refer to the Jason Hugh's link below and think about it.

Take out HV batt pack / cut out bad cell? (S P85+)

 

[rns-e]

Tesla - 'everything is fine, nothing to see here. Come back when it is out of warranty.'

Talking to Jason and trying to find someone who can help my friend with a raw can PT/CAN3 dump, which Jason has kindly offered to read and find the ammunition for the dialogue with Tesla.

Yes, that post describes very well what is happening

 

[David99]

A battery that shuts down at 10% and also won't charge to 100% is definitely defective. Tesla is really bad when it comes to issues with the battery, though. They are extremely reluctant about replacing batteries. I had a similar situation and Tesla also said it's all good.

People often don't understand that the BMS can't compensate for cells or groups that have aged and degraded differently. If one group or module is older or has degraded more, balancing can't compensate for that. It means one group or module simply can't store the same amount of energy as the others. And since they are all in a chain, the weakest link determines the total pack capacity. Once the weakest groups or module is down to zero, it doesn't matter how much the other ones have left. The car will shut down to prevent the weakest cells from going to zero and get completely damaged. That's likely what's happening here. The car shuts down at what it thinks is 10% but the weak brick/group is giving in.

The problem is, that's how all battery packs eventually die. One group is getting weak and forcing the entire pack to shut down early. Batteries don't last forever. That's just how they die. The question with the old packs is at what point does Tesla consider it a warranty case. They never made a clear statement. Starting with the Model 3 they clearly said 70% capacity is the threshold. But with the old S and X they never made it clear.

Tesla stopped making the old packs so they don't have a way to replace them. They also don't want to give people with legit warranty claims a brand new battery. That's not what a warranty is for. So they are denying warranties as much as they can and patch old batteries together.

 

[Rocky_H]

Tesla stopped making the old packs so they don't have a way to replace them.

Well, let's clarify that. They do have a way to replace them, but what they are replacing them with is not always exactly the same thing as was in there before. This new battery type that is about 90 kWh capacity but is made in a 350V configuration is a new thing that Tesla does build now and uses for warranty replacements on those older packs as needed if they don't have a refubished one available. But it's a battery type that they made later that was never included in any original cars.

 

[rns-e]

A battery that shuts down at 10% and also won't charge to 100% is definitely defective. Tesla is really bad when it comes to issues with the battery, though. They are extremely reluctant about replacing batteries. I had a similar situation and Tesla also said it's all good.

People often don't understand that the BMS can't compensate for cells or groups that have aged and degraded differently. If one group or module is older or has degraded more, balancing can't compensate for that. It means one group or module simply can't store the same amount of energy as the others. And since they are all in a chain, the weakest link determines the total pack capacity. Once the weakest groups or module is down to zero, it doesn't matter how much the other ones have left. The car will shut down to prevent the weakest cells from going to zero and get completely damaged. That's likely what's happening here. The car shuts down at what it thinks is 10% but the weak brick/group is giving in.

The problem is, that's how all battery packs eventually die. One group is getting weak and forcing the entire pack to shut down early. Batteries don't last forever. That's just how they die. The question with the old packs is at what point does Tesla consider it a warranty case. They never made a clear statement. Starting with the Model 3 they clearly said 70% capacity is the threshold. But with the old S and X they never made it clear.

Tesla stopped making the old packs so they don't have a way to replace them. They also don't want to give people with legit warranty claims a brand new battery. That's not what a warranty is for. So they are denying warranties as much as they can and patch old batteries together.

I think you're right about of the it. I my book 70% is useless, no battery is going to get below 70% in the warranty period unless it fails. And as Rocky_H said, there is a 350V 90 kWh option now, I have that in my car. It looks like my friend is finally getting somewhere with Tesla, but they will need it to fail again before going further with the case, so he will soon be cruising to see if it stops with 10% again.

 

[Rocky_H]

I roll my eyes when people try to drive down to that last gasp, and their car shuts off with 2 rated miles left or something, and they are throwing a fit. I just don't think people should expect that level of precision down to the last %. But a battery that consistently quits with 10-15% still showing is a failed battery. There is some kind of line somewhere in between those ends of the spectrum.