Removing A Bad Lithium Cell from Battery Pack, Smart Fortwo 

Great video. You don’t have to use the grinder, you can place your 5 in 1 between the tab and the plastic after you seperate the side that is not welded and pry a little as you separate the other side and the spot welds will pop right off.

You are indeed correct in regards to the cells needing structure. A safety designed in many lithium pouch cells to prevent thermal overrun or internal shortage is they are built with the "Active Material" sheets being loose between the anodes and cathodes. When pouch cells go bad, they swell and the separation in the layers basically self disables parts of the cell so it reduces to lower capacity or completely unable to hold a charge due to the spacing between the layers is no longer close enough to allow the flow of Ion transport. Basically, they are designed with chemical reaction built into the active layers to swell under the presence of certain chemicals, thus why you see swelling occurring. The swell reaction produces room for the sheets to reduce transfer energy internally. If you dont place the structuring back, the cells that are exposed to the void can expand under the heat of use and when an internal layer expands too much could trigger them to chemically react and permanently swell. I would just measure the thickness of a cell pack and just cut a thin wood spacer to slot between the cells in that empty space and assemble the pack back together, soldering a wire to continue the connection among the battery according to correct polarity.

All cells expand and contract (slightly) when you remove or add energy. This weakens the bond between the cathode and anode. Heavly compressing pouch cells helps to mitigate this somewhat. Tube cells (18650 ect) are wrapped on themselves to stop this. So in short, yes the cells will last much longer when compressed.

When using a grinder like that you should always have a face shield over the safety goggles. I'd recommend hearing protection too! Thank you for sharing these videos, I have one of these Smarts so I wanted to know how it worked and your video shows an otherwise impossible to find view.

I would leave the bad cell inside and just jumper over it, I would also discharge it to 0 volts very slowly.

Wonderful job David. I'll suggest you isolate/insulate the bad cells' contacts and return them back to the module.

They are tightly packed for structural purposes. (e.g., so they don't disfigure). I have 20Ah lifepo4 pouch cells loosely bound in a "giant usb battery" and they perform just fine without constriction. Though in my battery they're in a hard tool case surrounded by foam packing :-). Nice to see you wearing gloves for a change. Also a bit of gap from the exterior insulator and the cells isn't really a problem. You can do the same by putting tape on the cell and pulling it. Out of the factory they are firm due to adhesion (remember the cell is full of liquid electrolyte) but you can seperate it by pulling on it (source: I accidentally pulled on some tape I had on my pouch cells). I mean your cell is likely dead if it's reading 0 volts but just because the exterior is loose doesn't itself mean it's dead.

Get a piece of plastic or something similar size and thickness and fill it in. Thats not too bad that only a coulpe cells are bad. Thanks for sharing

Cutting boards to the rescue!

2:47 We thank you man.You give us such a valuable information :-).

You don't have to take the written voltage on the pack too literally. When the cells are fully charged, they will be 4.2 V, or preferably somewhere between 4.0 V and 4.1 V (4.2 V will cause faster degradation). But as they discharge, they will get closer to 3.0 V (never let them get discharged to 0 V). The written 3.6 V or 3.7 V is just the average voltage, or the voltage in the middle of the voltage range.

I'd find some non-conductive fiber/plastic type board to fill the space of the missing battery.

Do you have a fire extinguisher in your shop? If not, it would be a good idea to get one. Even if you, talk with your local fire department to make sure you have the correct class.

As others have suggested, either leave the bad cell in there, just cut the metal positive and negative connectors from it, or find some other piece of plastic to sandwich in between the cells to keep them pressed.

Did you get the 50Ah out of it? Litec.De made by AG Diamler. SK cell. I got a few of those. You can always tell where the puffing is. They are very sturdy, thick cells. Not very powerful. Also David, since I do alot of this: there is a Dremel head that is out, a new one that takes great little sturdy blades. I chop up a whole module with one or two disks. Great tool: Angle grinder is to strong here.. I used to do that but the danger of cell puncture is to great to risk getting burned. ( Gas. the "air" in the cell is called a "gas". ) ;)

The cells were pressed together like that to get the most cells in a contained space, I wouldn't worry about the gap.

David Do you mind sharing a link fo where you got the software for your balance board? The one amp guy you have in this video. I am asking due to that I have one OTW and would like to load and test it on this computer with blue tooth. Thanks. Btw Your videos have been a lot of fun following over the past few years. Thanks so much for letting us all be a part of this journey. God Bless..

Use the old pack but disconnected/bypass them from the Main cells. Hook up a 10k resistor with a heat sink to the dead cell for discharge! be careful if the cell start to get larger as it is not air in that cell it can be hydrogen, fluorine, and or other gases. Best to have a outdoor metal box with a vent.

How about threading those long rod ends a bit further so you can bolts them back up tight?

Leaving the cell out would create a hotspot where there's still standing air. Either replace it with a piece of heat-conductive material (metal or ceramic - maybe a ceramic tile) Also they need to be squished hard to work properly.

The 3.6V vs. 3.7V marking has something to do what state of charge (SOC) they are nominally with. They are still the same 4.2V full charge cells.

I thought you would remove the plastic frame as well... Also, I would have used a small Dremel probably, instead of the grinder.

great video, as always! one thing... those gloves are great, but if you accidentally short a lead out, the risk isn't only electrocution. You really should always wear eye protection! (and if you value your face, consider a face shield.) :)

take out 1 black spacer. the one from the cell you removed

Hello David, have you ever measured the cell resistance, I made my battery the same way you did, and the inverter has the menu point battery resistance and I don't know what value to enter there. I hope you can help, best wishes Paul

I thought you were about to take out the non-working cell and replace it with a working cell from the other pack to make them kind of equal in size

Hello, glad to be on your chanel. Maybe you know.. i have message on display my smart "hv system workshop" what can it be and what can i do with this? Even official service in my country cant help me..

you have to fill that gap if you want to use it at 1C or greater, im glad that you are able to use most the cells, will be cool to see how long they last long term. thanks for the upload, O yea hows you aims working, do you notice the 85w consent drain? I am testing the new reliable 8000w and its got a 35w idle drain, also wondering for my grand rents as they only have 1500w of solar :S

Do you have a fire extinguisher in your shop? or at least a plan if one of those cells catches fire (like drop it into a bucket then run the bucket outside).

where can i by the 3.6 cells of the smart fortwo?

Thanks for your experience!! So, do you have the "mounting" video???.... and the most interesting: Where do you buy "new" or used cells??? Regards!!

Hi what material is that white sheet between battery terminals and the cooling plate?

You look like Mickey Mouse with that black shirt and big white hands 😂🤣😂.

In a some videos I saw that people extracted the gas and after reseld the battery littium 18650 and get recharge a realive the batteries... but I dont know if that it´s works!

Would it be posibble to buy one new cell?

Hi David! I know this video is old, however I am looking for original Smart BMS. Do you have it by any chance?

I know this is a long time ago, but did you meassure the size of the battery modules? I am hoping max 48 cm lenght.

I know its been a while since your video, but would you have the dimensions of the battery case, with respect to how deep it is..I have a 2018 Smart and am planning on replacing just the cells with 100 ah units but need the dimensions to see if they will fit...thanks

I have one of these cars, can i but 2 or 3 cells from you? Spares would be good, supply part # there are diff versions

Any idea why both the cells that are bad are also next to each other? I don't think it's a coincidence.

Use the void for the BMS and pack it.

Put it back in but make it so it doesn't work (don't connect the tabs)

hi. Do you have spare parts for sale? The HV connector or the BMS box on front left? THNX.

I have a smart EQ battery with 20 000km and using the xentry diagnose on the car I discovered that one cell has 102mV less than the others.... also is telling me that the actuator is blocked...my question: the actuator is one of those 3 relays inside? Second question: can I balance the single cell charging a little the cell that has less (102mV less) and what voltage to use ? Ps: I don't want to disconnect the electronic board from the cell that needs charging....can do that?

what about a plastic cutting board to take up that space?

where can I buy those cells for my smart _?

The "air" inside is hydrogen.

I have two of these modules if someone interested in buying them :)

One day when we have the tech to send people to Mars and back, this is the type of person they will need to find.

heya yes that cell really doesn't look good

Install a peace of rubber the thickness of the cells you removed

Why don’t you cannibalize one pack and fix the 2 damaged ones

There is not a particolar reason why the lithium cell should be pressed, indeed in RC stuff they never are. The metal plate at the sides it’s to avoid punctures

Bubble wrap