Replacement Battery Model 3 long range with 22K miles.

[mvill]

I need some perspectives to help me get my mind wrapped around how Tesla handles service.

Situation:
Last week my partner ran over a deer that had been hit earlier causing the lines coolant to leak. The car drove and handled well, but gave the "Slow down" warning. We had it towed to a Tesla service center who said that the lines that feed the battery were damaged.
They say they can not fix the lines so we need to replace the entire battery assembly that is otherwise undamaged (part cost $13.5K).
Q1) Is there anyone who will replace just the coolant lines feeding the battery?
Q2) If so, does this affect the warranty?
Also, though we are paying for a replacement assembly $13.5K in full, they will not allow us to keep the "Damaged" part claiming it is "Restricted part".
Q3) Is this legal, can they really say that something I bought, I can not have? Been working on ICU vehicles 30 yrs and this has never heard anything like this.
Q4) When we do replace it, how do we make sure we get a like conditioned unit that has almost never been charged over 80% and only has 22K on it?

Thanks for your perspective.

 

[golfpilot]

This is probably what you broke. For some reason Tesla replaces the whole battery if you break the hose connector in the front. If you run something over it's going to hit the front of the battery. Front of the battery is this coolant line. It's not even a difficult fix.

I think what's happening is Tesla doesn't really have mechanics that solve problems. They have techs that just follow instructions and replace modules. They probably send the battery to depot level maintenance and they replace the connector.

If this were my car, and that is what broke, I would take the insurance money and fix the coolant line myself. What I'm most excited about is they are only charging 13k for a replacement battery.

 

[ElectricNerd]

If this were my car, and that is what broke, I would take the insurance money and fix the coolant line myself. What I'm most excited about is they are only charging 13k for a replacement battery.

It would still affect the resale value as the history would show a claim.

 

[Candleflame]

Maybe the BMS is much weaker in the Model 3 (Tesla did reduce phantom drain a lot), but from the Roadster days, my understanding is that each group of parallel cells (a brick) functions as a unit, so as long as cells are well matched in a group, it would work fine. You just do a rough manual balance before reassembling the pack.

The whole point of balancing is to handle differences in capacity among groups, so it's actually expected they aren't perfectly matched (although from factory they obviously try to ensure they are as close as possible, to minimize the amount balancing required, and to ensure maximum capacity).

Yes, you do lose capacity proportional to the amount of cells in parallel (in Roadster that means 1/69 if you lose one cell). Basically the total pack would be limited by the weakest group. In the Roadster, the battery had 11 sheets, so that basically functioned as a semi-independent unit (although there were 9 bricks per sheet, each with 69 cells).

From discussions elsewhere, service centers for Roadster have done various fixes including cutting out the bad cell, swapping only one sheet, or swapping the whole battery.
Need my roadster geniuses / Please Help Logs/ 1.5 not charging or battery issue?

I think the bigger problem with Model 3 pack is it is not built in a modular way, so removing individual cells, a group, or a bunch of groups is much harder. It seems to be split roughly in 1/4 (4680 look to be even less modular and is just one whole unit).

im not sure how closely the cells have to be matched - rich rebuilds says they never managed to get it right even using similarly degraded cells. The BMS relies on ultrasimilar degradation. It doesnt seem to matter at first but the pack will go more and more out of balance. and there is no good way to fix it. It seems that the battery modules arent designed to be replaced at all. If one module fails all have to be replaced.

 

[MP3Mike]

rich rebuilds says they never managed to get it right even using similarly degraded cells.

Do you happen to have a link to where he says that? I would really like to have that to point people to when they say his shop does battery repair by module replacement.

 

[wk057]

The cells in factory built original packs aren't perfectly matched, no of course not. That's impossible. The BMS has balancing circuitry for a reason.

BUT, they're matched well enough to be within the ability of the BMS to keep them in balance over an indefinite period of time under normal use. Unlike when mismatches are purposely introduced (replacing a module, cutting a cell, etc), the imbalances that happen "naturally", for lack of a better term, in a factory original pack are always going to be within the ability of the BMS to keep in check, especially since it's with the pack for the entire life of the battery to catch these imbalances early, learn which cell groups need the most work, and preemptively work on those as needed. It's quite complete, and not a "dumb" stateless system (the Roadster, for example, was closer to a "dumb" system, for example, which is why some more crude repair techniques may have some lasting functionality). Changing things like a whole module, or "remove" a cell, throws this completely out of whack, and the BMS might even make the situation worse for a while after because it thinks it's working on something that isn't the case anymore.

Even fully resetting (not something really doable easily, so don't worry) a BMS in a mature original pack can have detrimental consequences because the BMS has no way to know which groups are strongest/weakest and continue efforts to keep them in check. Instead it'll have to wait until there is an issue before it can begin correcting it. On something like a much older high mileage battery this might mean an impending failure, reduced capacity, etc.

Long story short, the S/3/X/Y BMS is pretty incredible. By far the best in the game. There's not even a contest. Nothing I've seen comes close. It's absolutely amazing at managing things it was designed to do. The main thing is that you can't give it a task it it wasn't designed to handle and expect everything to be peachy.

 

[Candleflame]

Do you happen to have a link to where he says that? I would really like to have that to point people to when they say his shop does battery repair by module replacement.

ok honestly maybe it wasnt rich rebuilds... but there was a big topic here about a model S battery module replacement where someone had a bad module which caused cell imbalancing and max charge reduction. The first time they put a fresh module in which worked really well but they started getting an imbalance very quickly.
Someone looked at the data and noticed that the pack struggled to maintain balance because 1 module had no degradation, but the other modules had like 10% degradation. So essentially everytime the owner charged the new module wouldnt charge and discharge at same rate - so the BMS almost immediately starts clamping down the max range.
They figured to just put a degradaded module instead so they put something in which was really similar i.e. lets say 9% degradation. Owner was fine for a few months but issue happened again. Apparently even a tiny difference causes huge problems. Its probably not just the degradation, cell-age itself probably causes different cell behaviour - different enough that the BMS struggles.

 

[3sr+buyer]

ok honestly maybe it wasnt rich rebuilds... but there was a big topic here about a model S battery module replacement where someone had a bad module which caused cell imbalancing and max charge reduction. The first time they put a fresh module in which worked really well but they started getting an imbalance very quickly.
Someone looked at the data and noticed that the pack struggled to maintain balance because 1 module had no degradation, but the other modules had like 10% degradation. So essentially everytime the owner charged the new module wouldnt charge and discharge at same rate - so the BMS almost immediately starts clamping down the max range.
They figured to just put a degradaded module instead so they put something in which was really similar i.e. lets say 9% degradation. Owner was fine for a few months but issue happened again. Apparently even a tiny difference causes huge problems. Its probably not just the degradation, cell-age itself probably causes different cell behaviour - different enough that the BMS struggles.

That is very interesting and surprising that the Tesla BMS cannot handle slight differences, when other EV BMSes can handle that without causing greater imbalance or degradation (but merely limiting capacity to that of the worst cell). Tesla seems to be ahead of others in so many ways with respect to electric-specific stuff that it seems odd that the BMS struggles in this situation that is entirely forseeable (and forseen in that if quality control lets through a bad cell that could cause a fire, the fire resistance features mostly prevent fires, although the car then has a dead cell that now causes an imbalance).

 

[MP3Mike]

Tesla seems to be ahead of others in so many ways with respect to electric-specific stuff that it seems odd that the BMS struggles in this situation that is entirely forseeable (and forseen in that if quality control lets through a bad cell that could cause a fire, the fire resistance features mostly prevent fires, although the car then has a dead cell that now causes an imbalance).

Which would you rather have a pack that loses 2-11% for every cell that fails or a pack where they replace it under warranty when a cell fails? I understand that your choice may change depending on if you are planning to keep the car out of warranty or not.

In other packs, like the Bolt, a single cell failing would result in a 33% capacity loss... They supposedly support module replacement but that failed and they ended up replacing entire packs. I don't know what other OEMs have done. They probably don't have enough volume to have experienced much yet.

 

[3sr+buyer]

Which would you rather have a pack that loses 2-11% for every cell that fails or a pack where they replace it under warranty when a cell fails? I understand that your choice may change depending on if you are planning to keep the car out of warranty or not.

In other packs, like the Bolt, a single cell failing would result in a 33% capacity loss... They supposedly support module replacement but that failed and they ended up replacing entire packs. I don't know what other OEMs have done. They probably don't have enough volume to have experienced much yet.

Ideally, you would want a BMS that can handle different capacity cells or modules (without increasing imbalance or degradation) like the Bolt's, but also have the car give a reliable indication of capacity (like the Model 3 when you look at the rated remaining range) so that you can get the battery replaced under warranty if the bad cell degrades the pack capacity below the warranty threshold.

The reason GM went to replacing entire Bolt batteries is that they eventually figured out that the fire defect could exist in all batteries or modules produced before around September 2021, and it was not possible to definitively determine which cells or modules did not have the defect, not because the Bolt BMS was unable to handle mixed module batteries that existed after some modules were replaced under earlier attempts to remove the fire defect (when they believed that they could determine which modules did and did not contain possible fire defects).

 

[wk057]

Ideally, you would want a BMS that can handle different capacity cells or modules

Makes no sense to design the BMS to handle gross voltage/CAC/impedance mismatches when 99.99% of the vehicles out there will never need hardware that can handle more than what the Tesla BMS already handles. The only time it would come into play is in the event of a failure which should lead to a pack replacement anyway, or from misinformed folks attempting repairs they shouldn't be attempting. The latter the designers shouldn't consider at all, and the former is rare enough that there's no need to overcomplicate designs based on it.

Plus, even if they did make the BMS able to handle some amount of gross mismatch, this is highly inefficient. You're either doing cell bleeding: a bunch of cell groups bled to compensate for a weak module, or a strong module bled to compensate for a weak pack... all of which is wasted as heat and can easily contribute to a major loss in useful capacity and overall efficiency (you thought vampire drain was bad before?). Alternatively, a way more complex system could be used to charge-shuffle between groups... but this is also inefficient, and has major drawbacks in large packs on cost, complexity, safety, and long term reliability. It just doesn't make sense from any POV really.

Edit/Add: There are also safety considerations with mismatched cell groups as well. Since the BMS can only measure cell voltages so quickly, in the case of a gross mismatch a cell group can quite easily be pushed into the upper or lower danger zone (ie: boom) before the BMS has time to react, especially if the BMS hasn't organically learned of a growing mismatch ahead of time. For example, let's say you swap in a weak module because one failed. Car is mostly charged, and you go for a drive. As you come to a stop, regen kicks in, and since that module is weaker it's immediately pushed over the max safe charge voltage in the series string. The BMS's bulk voltage is normal, since the rest of the pack is fine, but it takes some amount of time (possibly on the order of several seconds) to notice that the weak module is individually pushed too high, command the motor to let up, etc. (Or vice versa, with a stronger module and a weak pack.) In the meantime you've already pushed it too high, and your car is on fire from overcharging a cell group.

Just. Don't. Do. It.

In the case of a group/module failure, best situation is recycle and replace the entire pack, and this is unlikely to change any time soon.