Isn't the problem with parasitic charging? Suppose you had a bunch of used 18650 cells. To scale the electronics, they'll be wired up in parallel and/or series so the charging logic can be shared, but since the batteries are wildly mismatched, it results in parasitic charging.
> maintaining packs together
(This might already be happening, but I haven't heard about it) The big thing EVs need right now is standardized battery packs. It reduces replacement cost, takes away anxiety that a replacement will exist when you need it, and enables down-cycle uses like stationary storage.
I think that may be a trickier proposition than it appears.
Certainly a standard form factor for a pack would be helpful for a specific manufacturer (similar to building multiple cars on top of the same basic frame).
Some of the issues I think one runs into is battery chemistries are rapidly changing so even if the shape of the pack remains the same the performance of it is rather different depending on what is put inside.
Then even with standard form and chemistry one pack to another can be rather different depending on the history of it's use (age, charge cycles, driven hard).
There is second life storage applications currently, and still more research going into it now.
Personally I think smarter controls and smarter diagnostic and pack sorting will be more useful.
That is why you sort them.
Some recent research into that: https://www.sae.org/publications/technical-papers/content/20...
You can also consider maintaining packs together to avoid complicated disassembling processes.