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[princec]

Gotta give Zero credit for their latest battery enclosure, the boi's a unit all right as the yoof say.

Cas

[Specter]

YOOTs !!

[MVetter]

The potting was a response to the 2012 recalls because battery packs were oxidizing, shorting, and catching fire. Bryan and Luke, Zero's battery gurus, decided to go overkill to prevent or at least extremely minimize the chances of said fires happening again the same way. Does it make servicing a pack impossible? Yes. Does it add additional challenges when considering thermal management? Also yes.

Does it work? Also yes. So yeah, safety first. For whatever issues Zero may have, the packs are rugged and durable.

[T.S. Zarathustra]

Replacing the cells is not the easiest thing to do, that is for certain. Also dangerous. There is a very real risk of death by fire and/or electric shock. But it should be doable. The main thing IMO is the BMS. I understand it has ID that it communicates to the MBB, so simply replacing the BMS without reprograming the MBB would not work. It would be nice if someone can confirm if that is the case, or not. So it looks like it would be important to be able to reuse the BMS board (also cheaper).
All epoxies have so called "Glass transition" temperature. That means at certain temperatures they become flexible, or rubbery. In some cases, at certain temperatures, some types of Epoxy just peel of the part encased in it. I have successfully fixed more than one CDI unit by removing the epoxy and resolder or replace components. But each case is different and I have not tried to open the Zero battery case. Yet. I don't even know if the BMS is inside the battery, or covered in epoxy, or not. I find it difficult to find nice pictures of >2015 batteries that are partially disassembled. I've seen some glimpses in Doctorbass videos but not enough to build a full picture. At the moment this is theoretical to me. This would be something I would only attempt when the battery actually goes bad and I have nothing to lose. That might be many years in the future.
In theory, if you have a working BMS, all you have to do is connect the right number of cells, with roughly the right capacity. You don't have to reuse the Zero battery housing or cell layout. It might not be a perfect battery, but it would be better than a dead battery. There are number of Gen1 Zero battery packs that have been rebuilt this way.

[MVetter]

The BMS is on the front of the pack. You can easily take it off and replace it.

[ZeroChrissy]

They can do it...
https://kwsseuren.de/akku-reparatur-der-fahrradbatterie/zero

[T.S. Zarathustra]

The BMS is on the front of the pack. You can easily take it off and replace it.

Awesome. Thanks.

[T.S. Zarathustra]

This Zero Battery Teardown video was posted less than an hour ago. It's better if you speak German, but the pictures are in English.

After watching this I've come to the conclusion that rebuilding the pack is not a terribly complicated thing to do. Of course precautions must be followed to prevent fires and deaths.

Edit. It's not that I'm too concerned about the safety aspect. Any person with some understanding of electronics and moderate amount of common sense will not have issues. But not everyone has common sense, the potential for calamity is there, and people will nag if I don't mention it. 

[MVetter]

Ja, ja! Das busbar, das BMS, und das doghouse.

Max is a treasure.

[T.S. Zarathustra]

So, I was thinking. Never a good sign.

If I understand correctly. The monolith battery pack is made out of 4 modules. Each module has 28 cells in series. When the monolith is assembled, each cell in each module is connected in parallel to the equivalent number cell in the other three modules. Then to the BMS. If one cell in one module starts to go bad it would therefore be enough to remove that module (apparently there is thermal sensor but that can probably be substituted with a resistor). The capacity of the monolith would drop by 1/4th but with gentle use the bike should be usable for shorter distances without issues. Until a cell in the next module would go bad. But that might be 10 or 20000 km later.

Then there is the option of getting another bad monolith, and have the possibility to swap modules around to make one good monolith out of two bad ones. It will not last as long as new cells but it might extend the usable life of the bike for few more years.

Repeat as necessary. 

[Specter]

The problem with that is, as one cell goes bad, it tends to put a lot of stress on the cell next to it, which then goes bad because it's not getting charged properly, and the problem can rapidly cascade.

Cells in parallel, eventually will charge up, as their voltages go up and down / internal resistances etc, the current will go here and there until they all are at about an even level, a bad cell in parallel is not that huge a deal until it really goes bad.  Cells in series is where the problem lies, if one goes out of bounds, especially with this tech, where the voltage pretty much crashes, or skyrockets at the ends, a bad cell, will be detrimental to ones around it very quickly.  Over charging these cells, just a few times, can be VERY bad for them, and it won't take hours either, they can over charge very fast in the last percent or two, in a matter of a few minutes and if a bad cell is keeping the arm voltage low enough to force more current thru them, well, now we have a problem.

Aaron

[T.S. Zarathustra]

Exactly. If you take out the module with with bad series cell, and get another module from another monolith, the modules will be in parallel, so while not ideal solution, it should work for a while. Ideally you would balance all the cells within each module before assembly.

[Specter]

ideally you would have a balancing circuit built in because even though you do balance them on assembly they do still like to drift, and each cycle or  partial, they drift further.  Balancing circuits are so simple, and even buying balancers are fairly cheap and they can be piggy backed to as long of a string as you need really.  Although its a shitty way of doing it, you could, in theory balance one arm, and with parallel jumpers take that to the other arms too.  Me personally i like to balance each cell an not hunk a bunch of batts on one element.

Aaron