The cells are probably the hardest part of the system to manufacture. Damn near anyone can make a BMU (and they do), though there is a fair amount of effort needed to design a decent and affordable pack. Very few entities can make a decent lithium cell.

> Damn near anyone can make a BMU (and they do)

For small currents, yes. For the huge current spikes both in draining and charging, or the continuous massive loads of supercharging? No. Same for the actual science: figuring out a way to pull/push hundreds of amps to the pack while taking care that no single cell is overloaded/overheated or that faulty or degraded cells are taken care of.

No, making good cells is actually the hard part. The charging electronics is simple and easy. You can buy these ICs for cents from the usual suspects. Or does TESLA have some special, hard to circumvent, patent on the charging algo?

It's more than charging. It's cell monitoring, cooling, protection systems. EV Battery packs are complicated.

Making a BMS is by no means simple or cheap in the range of cents. It's hard to make good cells, but creating a good BMS, designing an easy way to at fuse wires, creating cooling bands and figuring out how to do so on a huge scale is just as hard

Tesla has promised not to stop anyone using its patents in furtherance of the same mission to accelerate the advent of sustainable transportation.

https://www.tesla.com/blog/all-our-patent-are-belong-you