Individual Battery Module Replacement with Degradation

[RocketGhost]

I know that the battery pack is comprised of several individual modules. The great thing about that is that if one module fails the whole pack doesn't need to be replaced. But I've been wondering about replacing individual modules down the road when the battery is degraded. Let's say your battery as a whole has lost 50% of its capacity. Can just one module be replaced to boost capacity a little bit? Seems to be a more cost effective way to extend the life of the truck.

Similarly, what if one module completely fails at 50% overall battery degradation. Can just that module be replaced?

I'm interested to know what Ford's technical guidance is. I know that there may be issues of the modules being balanced with each other. Maybe there is a built in system to compensate for it?

I also know that these batteries aren't likely to degrade quickly and it may even be hundreds of thousands of miles before it's an issue. It would be interesting to know whether an entire battery pack replacement would ever even be necessary.

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[GoodSam]

I would assume the cells will age fairly evenly. If you are dropping the battery pack due to degradation (say when it is down to only 70% of rated range, the 8 year / 100K mile warranty setpoint?), then I think one would want to replace all the modules.

It would be wonderful, ~5 years from now, if the replacements could have twice the capacity as the original batteries! I wonder if the cell voltage range will be the same (~2.75-4.25Vdc?) but the capacity is increased? Same chemistry?
https://evreporter.com/understanding-a-lithium-ion-cell-datasheet/

However, OEM prices would try to make one buy a whole new vehicle. Hope there will be some non-OEM companies that find ways of making cheaper, yet reliable next gen battery replacements.

 

[queuewho]

I would assume the cells will age fairly evenly. If you are dropping the battery pack due to degradation (say when it is down to only 70% of rated range, the 8 year / 100K mile warranty setpoint?), then I think one would want to replace all the modules.

It would be wonderful, ~5 years from now, if the replacements could have twice the capacity as the original batteries! I wonder if the cell voltage range will be the same (~2.75-4.25Vdc?) but the capacity is increased? Same chemistry?
https://evreporter.com/understanding-a-lithium-ion-cell-datasheet/

The future is bright, I think, for these first gen trucks, the pack design seems pretty good for repairability, there's not much that will rust, there's already a community around forscan and such. I think eventually we will see people swapping out the packs for whatever solid state stuff we have in 5-10 years.

 

[Heliian]

Should work just fine. We'll see what happens eventually.

 

[Calvin H-C]

Can just one module be replaced to boost capacity a little bit?

If that is possible, I suspect the process of doing that involves removing the entire battery pack to perform the module replacement.

I also suspect that would be more labour-intensive since full pack replacement only involves removal and installation of the new pack. The module replacement would involve all that plus pack disassembly and reassembly for the module replacement.

All this is dependant on the battery pack design which would vary from one vehicle to the next.

The question is: how much is the cost from labour and how much is parts? Module replacement should reduce the parts cost, but if the labour is more, it may not be cost effective, especially when considering that replacing a few modules today would be followed by replacing a few more in another year or two. It may be best to replace the full pack.

 

[subseavet]

Without going too deeply into this, I have background in battery design and technology. Replacing a single sell to try to improve range or overall available capacity of the entire battery system is not an ideal solution. You'll get a very minor initial improvement but the system as designed optimizes the entire battery as a whole for charge and discharge, not cell by cell. For safety reasons, the vehicle limitations will be set by the cell with the least capacity and not the new cell with the higher capacity. So your charge speed, charge limits, and overall battery discharge limit (based on cell voltages) will be set by the lowest performing or weakest cell. Trying to optimize a large battery made up of many cells is a huge engineering challenge. The equipment we have in passenger vehicles is very well made and well designed and for cost reasons, does not manage battery health at the single cell level. It optimizes your battery as a system. It's better for your battery, safety, and your vehicle. So when you need to replace the battery, the best way to do so is to replace the entire pack. Anything else is not worth the time or money. The only exception is if a single pack in the battery is bricked because it's measured health is below what is considered safe for continued use in a motor vehicle battery setting. Then that pack will be replaced. I hope this makes sense and is helpful. Let me know if it doesn't.

 

[GoodSam]

Without going too deeply into this, I have background in battery design and technology. Replacing a single sell to try to improve range or overall available capacity of the entire battery system is not an ideal solution. You'll get a very minor initial improvement but the system as designed optimizes the entire battery as a whole for charge and discharge, not cell by cell. For safety reasons, the vehicle limitations will be set by the cell with the least capacity and not the new cell with the higher capacity. So your charge speed, charge limits, and overall battery discharge limit (based on cell voltages) will be set by the lowest performing or weakest cell. Trying to optimize a large battery made up of many cells is a huge engineering challenge. The equipment we have in passenger vehicles is very well made and well designed and for cost reasons, does not manage battery health at the single cell level. It optimizes your battery as a system. It's better for your battery, safety, and your vehicle. So when you need to replace the battery, the best way to do so is to replace the entire pack. Anything else is not worth the time or money. The only exception is if a single pack in the battery is bricked because it's measured health is below what is considered safe for continued use in a motor vehicle battery setting. Then that pack will be replaced. I hope this makes sense and is helpful. Let me know if it doesn't.

I think Ford can see the Voltage of every cell in each of the 6 or 9 modules and if one cell is too low (just a few percent?) it calls for the module with that cell to be replaced. Why the Voltage of one cell being low causes such a worry and a call for replacement of a module, I do not know. Maybe like you say "vehicle limitations will be set by the cell with the least capacity" therefore Ford would be called out for limiting power available to less than 100%. I would think that they would try to get away with that by resetting the now limited max power available to 100%. Just like the warranty only guarantees the battery stays above 70% capacity?

 

[subseavet]

It is worth noting that in EV and vehicle batteries, when your displayed SoC is 100% charged, the actual battery is not close to 100% of its actual charge capacity. The ultimate reason for this is safety and the fact that battery manufacturing is still not a highly reliable/repeatable and precise process. Individual cells made in the same factory can vary widely in final build quality and still pass QC tests and be sold (and also be safe). Additionally extra capacity ensures the battery will meet minimum performance specs over a longer period of time without needing early replacement or maintenance.

If/when we are able to solve the battery manufacturing engineering challenges (something solid state batteries are taking a big step towards) you could see a jump in available capacity in the very same size battery by as much as 20-30%.

So why does low cell or module voltage require replacement?

You're absolutely right that the truck can monitor the voltage of every cell in a module and the module total and average voltage. A pack could need to be replaced when the module average voltage drops below the low voltage threshold or when any single cell in a module does so. This is because abnormally low cell or pack voltage is an early indicator of battery failure.

You have to charge a battery with a lower voltage at a lower rate for safety reasons to avoid exacerbating the cause of the failure with potentially catastrophic results. A battery system needs to be relatively balanced to perform well, especially in an automotive battery that experiences many rapid charge and discharge cycles through normal use. Tolerances for cell to cell or module to module differential voltage are kept fairly tight to prevent any chance of catastrophic failure under the most stressing/limiting normal use cases.

Many cells or modules that are no longer suitable for EV batteries can be reused in other storage battery solutions with a slower and more predictable charge and discharge rate (home or grid storage batteries for example) so your "dead" pack is usually reused again before being recycled.

Batteries are really cool!

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