If you’re into BMS systems at all, you know that the ridiculous levels of modeling are chemistry / cell specific, to the point that would make the typical layman’s eyes glaze over. A litany of cell types (NMC, LiFePo4, NCA) and more as new chemistries are invented (or go in and out of fashion) requires updates to BMS, the modeling of how the internals of the cells work, and how all of that is related to the voltage/current/temperatures of individual cells.
Measuring voltage/current? Yeah, that’s easy.
INTERPRETING voltage/current? That’s the hard part. And requires a giant mess of R&D effort on these cells and their individual chemistries.
There’s nothing “simple” about that battery pack. The shear number of control systems that go into a modern battery-pack it should be proof enough to you.
Not only is there difficulty in building and manufacturing this… there’s also difficulty in maintaining this item. I mean yeah, we don’t maintain it, its just replaced wholesale. But there’s also the whole 400V will-instantly-kill-a-technician problem if they’re not careful.