The electrochemical interface where lithium intercolates into the anode and cathode of the battery experiences microscopic electric field variations that, depending on the local surface geometry, lead to side reactions and battery degradation. The hardware that converts DC to DC and DC to AC must be designed to mitigate the voltage ripple and harmonics that exacerbate the localized electric field extremes that prematurely degrade electrode interfaces and battery electrolytes. State of the art BMS and rectifier components are much more difficult to build than you might think.

Correct me if I'm wrong but your comments do not suggest that the end result of this engineering cannot be very simple, elegant, and hopefully even inexpensive if built at scale. Instead, they suggest that the team who builds it needs to know what the heck they're doing.

No argument here. What are we even talking about?

I think we're generally talking about the same thing. A complex piece of power electronics and software.