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

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(1) Except as provided in paragraph (2) warranty period relating to an implied or express warranty accompanying a sale or consignment for sale of consumer goods selling for fifty dollars ($50) or more shall automatically be tolled for the period from the date upon which the buyer either (1) delivers nonconforming goods to the manufacturer or seller for warranty repairs or service or (2), pursuant to subdivision (c) of Section 1793.2 or Section 1793.22, notifies the manufacturer or seller of the nonconformity of the goods up to, and including, the date upon which (1) the repaired or serviced goods are delivered to the buyer, (2) the buyer is notified the goods are repaired or serviced and are available for the buyer's possession or (3) the buyer is notified that repairs or service is completed, if repairs or service is made at the buyer's residence.

Fairly certain if your car has been in the shop for more than 12 whole days in the last 8 years for warranty repairs you are still under warranty. Start a new service request at a different service center and let them know that you know your rights. I bet they will “goodwill” the repair since they are likely legally obligated to complete it anyways.
Interesting indeed. So it sounds like this would potentially help OP if they were in California and could document 12 days the car was at the service center for warranty repairs. Less useful in Sweden but I suppose it's feasible they have a similar protection.

 
If you want a very large and expensive paperweight instead of a drivable car, continue on and "cut" cells out of your pack.

If you want a working vehicle, replace the entire pack.

There are no exceptions to this, despite claims by people on YouTube.

Is the Tesla BMS just picky and doesn't know how to deal with a pack missing a cell or with a replacement module?
How are the Tesla battery modules usable in something like an EV conversion if they must be so perfectly matched?
 
Is the Tesla BMS just picky and doesn't know how to deal with a pack missing a cell or with a replacement module?
How are the Tesla battery modules usable in something like an EV conversion if they must be so perfectly matched?
I bet you probably hear less about one off conversions using mismatched tesla packs (as in, the converter doesnt probe forums with basic questions and often expects issues like that so doesnt "complain" about it)

I couldnt hold a candle to Jason's knowledge on the topic, but I'd treat each battery pack like an aged fine wine, brought together by the sum of its parts. You cannot mix bottles of wine, even if they are from the same producer and of the same vintage but from different casks. To a trained pallet, you'd be soured.

I personally wouldnt gamble with my daily driver, or even my backup, knowing my pack has pushed out 160K without issues, to simply swap another module in and expect it to work in harmony with other or older batteries would be silly. Same reason you dont just swap in a brand new 12v to an existing system (likely?) it just brings your brand spankin new battery down to the level of the older batteries/system.
 
Is the Tesla BMS just picky and doesn't know how to deal with a pack missing a cell or with a replacement module?

It's not that it's too "picky" or anything. The BMS's only ability to influence balancing is to enable a 100mA dump load via bleeder resistors on individual bricks (74 cells). This is miniscule when looking at the whole pack, and with good reason. Once the pack is out of balance beyond the ability of the bleeder resistors to keep it in check, the pack likely has an underlying issue that should be dealt with.

Under normal conditions, the 100mA bleeders are actually overkill for bringing a pack that's aged normally into balance within a reasonable amount of time. In real world use with a regular pack, the balancers are actually pretty rarely enabled for more than an hour or so, and usually only on a handful of bricks. Even the oldest highest mileage packs naturally remain very tightly balanced with minimal assist from the BMS.

Removing just one cell from a brick means every other brick's bleeders need to run for about a full 32 hrs per charge cycle to keep the pack in balance. (We'll ignore that this means wasting ~1-2% SoC just for balancing...) So every ~1 hr of use the car needs at least ~8 hours rest for balancing to stay in check. And that's just with one cell missing!

Assuming the BMS doesn't pick up on this immediately and the car is actually usable initially, any time you drive more than a cycle per 32 hours (like on a trip where you hit a few superchargers), you bring the pack more and more out of balance, somewhat exponentially depending on how good the pack is. This is why the YouTuber guy who had one of the other YouTuber guys "fix" his car with a module swap ended up stranded on the side of the road with the dash showing 30+ miles of range. The pack reached a critical threshold of imbalance under load and the BMS was like, "nope!"

This is the inevitable result of any pack modified by removing cells or swapping in mismatched modules. It will die unexpectedly and generally without warning. Assuming it works at all initially, it could be days or months before it does, but it will stop working. Every. Single. Time. Doesn't matter how well you think you've matched modules. Once the BMS detects an uncorrectable imbalance, it will eventually cease to allow it to be used.

Things like the cell-level fuses are there as a safety mechanism. If a cell level fuse pops in normal use, that's cause for concern, and the BMS rightfully will make a fuss about it. When you do something dumb like literally break a fuse on the pack and cause the same damage that would be caused by something like a shorted cell, the BMS has no idea this is intended, detects the issue, and the end result is the same.

The packs are built to be safe. They're not built to be modularly repaired, and not built so that they can lose cells and still be used RAID style. That's not how it was designed at all. If there's an issue with a cell or cells, the pack needs to be replaced as a whole and that's the only real solution to such problems.

How are the Tesla battery modules usable in something like an EV conversion if they must be so perfectly matched?
Addressing this specifically, everyone I'm aware of using these modules in EV conversions is using modules from the same original pack, so they are perfectly matched. For example, when you order modules from 057tech, you always get modules from the same original pack (unless > 16, of course... then we do our best to match them closely, even though the use case likely isn't a series set at that point).

Also, a lot of EV conversions are lower voltage than Tesla, meaning modules can be parallelized with fewer modules in series. You can put mismatched modules in parallel without much issue, since voltage in parallel sets is a constant and the modules will naturally charge/discharge based on their real viability.

I bet you probably hear less about one off conversions using mismatched tesla packs (as in, the converter doesnt probe forums with basic questions and often expects issues like that so doesnt "complain" about it)

I couldnt hold a candle to Jason's knowledge on the topic, but I'd treat each battery pack like an aged fine wine, brought together by the sum of its parts. You cannot mix bottles of wine, even if they are from the same producer and of the same vintage but from different casks. To a trained pallet, you'd be soured.

I personally wouldnt gamble with my daily driver, or even my backup, knowing my pack has pushed out 160K without issues, to simply swap another module in and expect it to work in harmony with other or older batteries would be silly. Same reason you dont just swap in a brand new 12v to an existing system (likely?) it just brings your brand spankin new battery down to the level of the older batteries/system.

This is actually a pretty good analogy.

Every battery pack has aged differently. From the factory, the cells are all a little tiny bit mismatched, but all from the same batch of cells. So they'll quickly find their place within the whole and stay there, with a little nudge from the BMS occasionally, for the life of the pack without issue.

When trying to mix and match, things like mileage don't matter. Cycles don't matter. Capacity doesn't matter. How hard or lightly it's been driven doesn't matter. It's every factor combined over the entire life of the pack that determines how it ages and how it will continue to perform. You might be able to get a module that has a very similar total capacity to the rest of a pack, or even get it to balance pretty well with the rest of the modules. But, it's impossible for a replacement module to perfectly match the rest of the pack. Things will always be slightly off, and because these bricks are in a large series set these differences always result in a feedback loop that amplifies the differences over time no matter how small the differences are... and that's just how it is. You don't mix and match cells in series because current under load/charge is constant in a series string by definition. With mismatched modules you end up with the same current at different loaded voltages, resulting in unequal power/energy distribution throughout the pack, resulting in an imbalance.

I could go on and on about the details, but suffice it to say many have tried (myself included), and all have failed. I've tried this several times, always thinking I've gotten close enough to beat the BMS (or, well, physics/chemistry)... and every time the result has eventually been failure. The difference between me and others seems to be that the folks who've been super public about their miracle battery fixes never follow up with the failure portion of the "repair"... 🙄
 
It's not that it's too "picky" or anything. The BMS's only ability to influence balancing is to enable a 100mA dump load via bleeder resistors on individual bricks (74 cells). This is miniscule when looking at the whole pack, and with good reason. Once the pack is out of balance beyond the ability of the bleeder resistors to keep it in check, the pack likely has an underlying issue that should be dealt with.

Under normal conditions, the 100mA bleeders are actually overkill for bringing a pack that's aged normally into balance within a reasonable amount of time. In real world use with a regular pack, the balancers are actually pretty rarely enabled for more than an hour or so, and usually only on a handful of bricks. Even the oldest highest mileage packs naturally remain very tightly balanced with minimal assist from the BMS.

Removing just one cell from a brick means every other brick's bleeders need to run for about a full 32 hrs per charge cycle to keep the pack in balance. (We'll ignore that this means wasting ~1-2% SoC just for balancing...) So every ~1 hr of use the car needs at least ~8 hours rest for balancing to stay in check. And that's just with one cell missing!

Assuming the BMS doesn't pick up on this immediately and the car is actually usable initially, any time you drive more than a cycle per 32 hours (like on a trip where you hit a few superchargers), you bring the pack more and more out of balance, somewhat exponentially depending on how good the pack is. This is why the YouTuber guy who had one of the other YouTuber guys "fix" his car with a module swap ended up stranded on the side of the road with the dash showing 30+ miles of range. The pack reached a critical threshold of imbalance under load and the BMS was like, "nope!"

This is the inevitable result of any pack modified by removing cells or swapping in mismatched modules. It will die unexpectedly and generally without warning. Assuming it works at all initially, it could be days or months before it does, but it will stop working. Every. Single. Time. Doesn't matter how well you think you've matched modules. Once the BMS detects an uncorrectable imbalance, it will eventually cease to allow it to be used.

Things like the cell-level fuses are there as a safety mechanism. If a cell level fuse pops in normal use, that's cause for concern, and the BMS rightfully will make a fuss about it. When you do something dumb like literally break a fuse on the pack and cause the same damage that would be caused by something like a shorted cell, the BMS has no idea this is intended, detects the issue, and the end result is the same.

The packs are built to be safe. They're not built to be modularly repaired, and not built so that they can lose cells and still be used RAID style. That's not how it was designed at all. If there's an issue with a cell or cells, the pack needs to be replaced as a whole and that's the only real solution to such problems.


Addressing this specifically, everyone I'm aware of using these modules in EV conversions is using modules from the same original pack, so they are perfectly matched. For example, when you order modules from 057tech, you always get modules from the same original pack (unless > 16, of course... then we do our best to match them closely, even though the use case likely isn't a series set at that point).

Also, a lot of EV conversions are lower voltage than Tesla, meaning modules can be parallelized with fewer modules in series. You can put mismatched modules in parallel without much issue, since voltage in parallel sets is a constant and the modules will naturally charge/discharge based on their real viability.



This is actually a pretty good analogy.

Every battery pack has aged differently. From the factory, the cells are all a little tiny bit mismatched, but all from the same batch of cells. So they'll quickly find their place within the whole and stay there, with a little nudge from the BMS occasionally, for the life of the pack without issue.

When trying to mix and match, things like mileage don't matter. Cycles don't matter. Capacity doesn't matter. How hard or lightly it's been driven doesn't matter. It's every factor combined over the entire life of the pack that determines how it ages and how it will continue to perform. You might be able to get a module that has a very similar total capacity to the rest of a pack, or even get it to balance pretty well with the rest of the modules. But, it's impossible for a replacement module to perfectly match the rest of the pack. Things will always be slightly off, and because these bricks are in a large series set these differences always result in a feedback loop that amplifies the differences over time no matter how small the differences are... and that's just how it is. You don't mix and match cells in series because current under load/charge is constant in a series string by definition. With mismatched modules you end up with the same current at different loaded voltages, resulting in unequal power/energy distribution throughout the pack, resulting in an imbalance.

I could go on and on about the details, but suffice it to say many have tried (myself included), and all have failed. I've tried this several times, always thinking I've gotten close enough to beat the BMS (or, well, physics/chemistry)... and every time the result has eventually been failure. The difference between me and others seems to be that the folks who've been super public about their miracle battery fixes never follow up with the failure portion of the "repair"... 🙄

Interesting. I wasn't expecting such a detailed reply!

So what you would do with a pack with a bad module is just remove the whole module and re-use the remaining ones for a different use case.

With the 3/Y and refresh S/X packs with just 4/5 modules, this makes the packs way less re-usable in the case of a bad cell right?
 
@wk057 I LOVE Reading your posts and envy your knowledge. Ive read so many things/opinions, etc on charging, battery life, battery performance, and the science behind them. Definitely respect your opinion and your business. Couple of questions:

- Is it best to plug in every night/keep the car plugged in? Even if say, I've only used a couple % of charging that day? Or is it better to charge fewer times but for longer durations? Or does it really matter long term?
- Right now I drive maybe an average of 20 miles per day at most. (average). I plug in nightly to a max of about 60% charge limit. 4 times per year maybe to 100% for road trips. Supercharge maybe 2 times per year, if that. Any real benefit in charging to say, 40% per night? Or are we splitting hairs at that point

Thanks.
 
It's not that it's too "picky" or anything. The BMS's only ability to influence balancing is to enable a 100mA dump load via bleeder resistors on individual bricks (74 cells). This is miniscule when looking at the whole pack, and with good reason. Once the pack is out of balance beyond the ability of the bleeder resistors to keep it in check, the pack likely has an underlying issue that should be dealt with.

Under normal conditions, the 100mA bleeders are actually overkill for bringing a pack that's aged normally into balance within a reasonable amount of time. In real world use with a regular pack, the balancers are actually pretty rarely enabled for more than an hour or so, and usually only on a handful of bricks. Even the oldest highest mileage packs naturally remain very tightly balanced with minimal assist from the BMS.

Removing just one cell from a brick means every other brick's bleeders need to run for about a full 32 hrs per charge cycle to keep the pack in balance. (We'll ignore that this means wasting ~1-2% SoC just for balancing...) So every ~1 hr of use the car needs at least ~8 hours rest for balancing to stay in check. And that's just with one cell missing!

Assuming the BMS doesn't pick up on this immediately and the car is actually usable initially, any time you drive more than a cycle per 32 hours (like on a trip where you hit a few superchargers), you bring the pack more and more out of balance, somewhat exponentially depending on how good the pack is. This is why the YouTuber guy who had one of the other YouTuber guys "fix" his car with a module swap ended up stranded on the side of the road with the dash showing 30+ miles of range. The pack reached a critical threshold of imbalance under load and the BMS was like, "nope!"

This is the inevitable result of any pack modified by removing cells or swapping in mismatched modules. It will die unexpectedly and generally without warning. Assuming it works at all initially, it could be days or months before it does, but it will stop working. Every. Single. Time. Doesn't matter how well you think you've matched modules. Once the BMS detects an uncorrectable imbalance, it will eventually cease to allow it to be used.

Things like the cell-level fuses are there as a safety mechanism. If a cell level fuse pops in normal use, that's cause for concern, and the BMS rightfully will make a fuss about it. When you do something dumb like literally break a fuse on the pack and cause the same damage that would be caused by something like a shorted cell, the BMS has no idea this is intended, detects the issue, and the end result is the same.

The packs are built to be safe. They're not built to be modularly repaired, and not built so that they can lose cells and still be used RAID style. That's not how it was designed at all. If there's an issue with a cell or cells, the pack needs to be replaced as a whole and that's the only real solution to such problems.


Addressing this specifically, everyone I'm aware of using these modules in EV conversions is using modules from the same original pack, so they are perfectly matched. For example, when you order modules from 057tech, you always get modules from the same original pack (unless > 16, of course... then we do our best to match them closely, even though the use case likely isn't a series set at that point).

Also, a lot of EV conversions are lower voltage than Tesla, meaning modules can be parallelized with fewer modules in series. You can put mismatched modules in parallel without much issue, since voltage in parallel sets is a constant and the modules will naturally charge/discharge based on their real viability.



This is actually a pretty good analogy.

Every battery pack has aged differently. From the factory, the cells are all a little tiny bit mismatched, but all from the same batch of cells. So they'll quickly find their place within the whole and stay there, with a little nudge from the BMS occasionally, for the life of the pack without issue.

When trying to mix and match, things like mileage don't matter. Cycles don't matter. Capacity doesn't matter. How hard or lightly it's been driven doesn't matter. It's every factor combined over the entire life of the pack that determines how it ages and how it will continue to perform. You might be able to get a module that has a very similar total capacity to the rest of a pack, or even get it to balance pretty well with the rest of the modules. But, it's impossible for a replacement module to perfectly match the rest of the pack. Things will always be slightly off, and because these bricks are in a large series set these differences always result in a feedback loop that amplifies the differences over time no matter how small the differences are... and that's just how it is. You don't mix and match cells in series because current under load/charge is constant in a series string by definition. With mismatched modules you end up with the same current at different loaded voltages, resulting in unequal power/energy distribution throughout the pack, resulting in an imbalance.

I could go on and on about the details, but suffice it to say many have tried (myself included), and all have failed. I've tried this several times, always thinking I've gotten close enough to beat the BMS (or, well, physics/chemistry)... and every time the result has eventually been failure. The difference between me and others seems to be that the folks who've been super public about their miracle battery fixes never follow up with the failure portion of the "repair"... 🙄

Interesting stuff. Sounds very grim though. Also sounds like a serious design weakness.

Is Tesla even capable of replacing a module? Do they even try? Are their remanufactured packs just packs that had very minor issues that didn't involve cell failure?
 
Interesting stuff. Sounds very grim though. Also sounds like a serious design weakness.

Is Tesla even capable of replacing a module? Do they even try? Are their remanufactured packs just packs that had very minor issues that didn't involve cell failure?

Not really a design flaw. There's no way to design around this.

1654014729333.png


Remanufactured packs are ones that didn't have cell issues. Just hardware issues (BMS-related).

They also remanufacture 16 module packs (85/90/100) into 14 module packs (70/75/"New" 85) regularly when there is an issue at the cell/module level.

They did attempt module replacements at one point... but quickly stopped due to the issues above. They even tried to loosen some BMS parameters to make it more viable but eventually stopped this entirely and every pack this was done to was replaced again.
 
wk057 is the expert! My understanding is if a pack has a BMS electronics failure, these are factory repaired and used as a remanufactured pack. Contactors and Pyro fuses are also repaired, but this can usually be done on the pack at service - no need to send it to the factory or do a factory exchange.
 
wk057 is the expert! My understanding is if a pack has a BMS electronics failure, these are factory repaired and used as a remanufactured pack. Contactors and Pyro fuses are also repaired, but this can usually be done on the pack at service - no need to send it to the factory or do a factory exchange.

It seems like it should be possible to do those repairs at an SC but in the threads I've read here I've never heard of that. It's always Tesla quoting 12k to 25k or something for a replacement pack.
 
It seems like it should be possible to do those repairs at an SC but in the threads I've read here I've never heard of that. It's always Tesla quoting 12k to 25k or something for a replacement pack.
Yep. If they have a refurb pack avail, its the lower amount. If they dont and have to use a new pack, that higher amount
 
It's not that it's too "picky" or anything. The BMS's only ability to influence balancing is to enable a 100mA dump load via bleeder resistors on individual bricks (74 cells). This is miniscule when looking at the whole pack, and with good reason. Once the pack is out of balance beyond the ability of the bleeder resistors to keep it in check, the pack likely has an underlying issue that should be dealt with.

Under normal conditions, the 100mA bleeders are actually overkill for bringing a pack that's aged normally into balance within a reasonable amount of time. In real world use with a regular pack, the balancers are actually pretty rarely enabled for more than an hour or so, and usually only on a handful of bricks. Even the oldest highest mileage packs naturally remain very tightly balanced with minimal assist from the BMS.

Removing just one cell from a brick means every other brick's bleeders need to run for about a full 32 hrs per charge cycle to keep the pack in balance. (We'll ignore that this means wasting ~1-2% SoC just for balancing...) So every ~1 hr of use the car needs at least ~8 hours rest for balancing to stay in check. And that's just with one cell missing!

Assuming the BMS doesn't pick up on this immediately and the car is actually usable initially, any time you drive more than a cycle per 32 hours (like on a trip where you hit a few superchargers), you bring the pack more and more out of balance, somewhat exponentially depending on how good the pack is. This is why the YouTuber guy who had one of the other YouTuber guys "fix" his car with a module swap ended up stranded on the side of the road with the dash showing 30+ miles of range. The pack reached a critical threshold of imbalance under load and the BMS was like, "nope!"

This is the inevitable result of any pack modified by removing cells or swapping in mismatched modules. It will die unexpectedly and generally without warning. Assuming it works at all initially, it could be days or months before it does, but it will stop working. Every. Single. Time. Doesn't matter how well you think you've matched modules. Once the BMS detects an uncorrectable imbalance, it will eventually cease to allow it to be used.

Things like the cell-level fuses are there as a safety mechanism. If a cell level fuse pops in normal use, that's cause for concern, and the BMS rightfully will make a fuss about it. When you do something dumb like literally break a fuse on the pack and cause the same damage that would be caused by something like a shorted cell, the BMS has no idea this is intended, detects the issue, and the end result is the same.

The packs are built to be safe. They're not built to be modularly repaired, and not built so that they can lose cells and still be used RAID style. That's not how it was designed at all. If there's an issue with a cell or cells, the pack needs to be replaced as a whole and that's the only real solution to such problems.


Addressing this specifically, everyone I'm aware of using these modules in EV conversions is using modules from the same original pack, so they are perfectly matched. For example, when you order modules from 057tech, you always get modules from the same original pack (unless > 16, of course... then we do our best to match them closely, even though the use case likely isn't a series set at that point).

Also, a lot of EV conversions are lower voltage than Tesla, meaning modules can be parallelized with fewer modules in series. You can put mismatched modules in parallel without much issue, since voltage in parallel sets is a constant and the modules will naturally charge/discharge based on their real viability.



This is actually a pretty good analogy.

Every battery pack has aged differently. From the factory, the cells are all a little tiny bit mismatched, but all from the same batch of cells. So they'll quickly find their place within the whole and stay there, with a little nudge from the BMS occasionally, for the life of the pack without issue.

When trying to mix and match, things like mileage don't matter. Cycles don't matter. Capacity doesn't matter. How hard or lightly it's been driven doesn't matter. It's every factor combined over the entire life of the pack that determines how it ages and how it will continue to perform. You might be able to get a module that has a very similar total capacity to the rest of a pack, or even get it to balance pretty well with the rest of the modules. But, it's impossible for a replacement module to perfectly match the rest of the pack. Things will always be slightly off, and because these bricks are in a large series set these differences always result in a feedback loop that amplifies the differences over time no matter how small the differences are... and that's just how it is. You don't mix and match cells in series because current under load/charge is constant in a series string by definition. With mismatched modules you end up with the same current at different loaded voltages, resulting in unequal power/energy distribution throughout the pack, resulting in an imbalance.

I could go on and on about the details, but suffice it to say many have tried (myself included), and all have failed. I've tried this several times, always thinking I've gotten close enough to beat the BMS (or, well, physics/chemistry)... and every time the result has eventually been failure. The difference between me and others seems to be that the folks who've been super public about their miracle battery fixes never follow up with the failure portion of the "repair"... 🙄
Thanks for the explanation wk057.

If Tesla can refurbish a 16 module pack (85,90,100kwh packs) to 14 module packs, why is that not done by DIYers and repair shops? Cannot the main BMS board be reprogramed as a 15 or more likely, as a 14 module pack with a corresponding 2/16 drop in range?
 
Thanks for the explanation wk057.

If Tesla can refurbish a 16 module pack (85,90,100kwh packs) to 14 module packs, why is that not done by DIYers and repair shops? Cannot the main BMS board be reprogramed as a 15 or more likely, as a 14 module pack with a corresponding 2/16 drop in range?

Nope. The BMS board needs to be replaced, as the required configuration items are OTP (one-time-programmable). You can't reprogram certain things on the BMS, unfortunately. Not even Tesla can do this. Since the main BMS is replaced, generally the shunt needs replacing as well since they're calibrated when paired.

We've done this. We we have BMS hardware from relevant 14-module battery packs because we handle hundreds of batteries per year. I don't think many, if any, other places would have such an inventory, and it's not something you can buy from Tesla.
 
Nope. The BMS board needs to be replaced, as the required configuration items are OTP (one-time-programmable). You can't reprogram certain things on the BMS, unfortunately. Not even Tesla can do this. Since the main BMS is replaced, generally the shunt needs replacing as well since they're calibrated when paired.

We've done this. We we have BMS hardware from relevant 14-module battery packs because we handle hundreds of batteries per year. I don't think many, if any, other places would have such an inventory, and it's not something you can buy from Tesla.
im just glad you're back in action! :D
 
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Nope. The BMS board needs to be replaced, as the required configuration items are OTP (one-time-programmable). You can't reprogram certain things on the BMS, unfortunately. Not even Tesla can do this. Since the main BMS is replaced, generally the shunt needs replacing as well since they're calibrated when paired.

We've done this. We we have BMS hardware from relevant 14-module battery packs because we handle hundreds of batteries per year. I don't think many, if any, other places would have such an inventory, and it's not something you can buy from Tesla.
Wow, so if you have a 85kw pack and a module happens to fail for some reason, or a bms fails, the whole pack basically has to be replaced. You can't remove one of the 5kw modules and stick with the remaining 80kw... I have a new battery pack in my 2013 p85 model s that cost $14k and this honestly makes me want to just sell my Tesla and be done with it when I hear this. I'll go buy something else under warranty for 8 years non-tesla. BTW, I'm an EE and do automotive electronics for a living... the person who thought a one time OTP flash programming on a bms was a good idea has cost Tesla and owners millions in pack replacements.
 
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Wow, so if you have a 85kw pack and a module happens to fail for some reason, or a bms fails, the whole pack basically has to be replaced. You can't remove one of the 5kw modules and stick with the remaining 80kw... I have a new battery pack in my 2013 p85 model s that cost $14k and this honestly makes me want to just sell my Tesla and be done with it when I hear this. I'll go buy something else under warranty for 8 years non-tesla. BTW, I'm an EE and do automotive electronics for a living... the person who thought a one time OTP flash programming on a bms was a good idea has cost Tesla and owners millions in pack replacements.
I think its also just battery chemistry. I don't mix batteries in my RV, if one fails i have to replace them all, or the new one will just be balanced down to the old ones. I am NOT an EE so... maybe an old wives tale but made sense to me
 
I think its also just battery chemistry. I don't mix batteries in my RV, if one fails i have to replace them all, or the new one will just be balanced down to the old ones. I am NOT an EE so... maybe an old wives tale but made sense to me
My point here is that the BMS was designed to not allow downgrading of the pack on repairs (It's programmed for the full pack capacity, and cannot be modified based on Jason's (wk057's post) due to OTP flash. If a single cell in a module fails out of the 7000 or so cells in total, the pack is done and prepare to write a $15k check to Tesla for R&R if out of warranty. If BMS programming was an option, you could remove the bad module and downgrade by 5kw. The 85kw pack would become 80 or 75kwh based on the remaining modules and repairs could be performed without swapping out the entire pack with the remaining balancing still remaining. There is obviously going to be a timeframe where too many cells are damaged or end of life, but when I hear about the numerous pack failures in the 50k range as documented here on the board, this would change the repair cost from 15k to $3k bill if the customer is fine with the smaller pack for a few years until complete replacement is necessary. It might extend the life of a pack past the 12 year mark. You probably would only be able to do this once or twice and downgrade to a 80,75,70kw from a 85 pack before the added current on all the cells will accelerate the wear. If I keep my ride I will be adding the warranty from wk057 past the warranty date on the replacement pack on my car.
 
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Reactions: cleverscreenam
I have some ways around the OTP issue, but it's definitely not ideal.
So basically other than swapping a bms from another battery, reducing battery capacity vs. swapping out the entire pack is not really an option for a single cell failure in the entire pack is what I think you're trying to say. Is this workaround a software/can hack or hardware R&R removal, copy flash to a file, reprogram flash chip and place it back on the pcb?