> Shouldn't this be a once-off cost per battery-pack version?
A BMS isn't just software. It requires a µC, voltage and temperature sensors for cell monitoring, and power electronics for cell balancing. However, those are all comparatively cheap, especially at scale, and the quoted cost of 50–75 US$/kWh looks ridiculously overpriced to me.
I expect EV batteries to have all those components preinstalled already, and naively thought the grid-integration involves reverse engineering the battery's protocol, and perhaps bypassing/replacing a µC or 3.
A BMS isn't just software. It requires a µC, voltage and temperature sensors for cell monitoring, and power electronics for cell balancing. However, those are all comparatively cheap, especially at scale, and the quoted cost of 50–75 US$/kWh looks ridiculously overpriced to me.