> Whilst cranking, an ICE car will drop to around 6 volts (then maximum power is extracted according to thevenim's theorem).

> That means all computers etc will work at 6v.

Not necessarily all of them. Plenty of stuff will drop out while cranking; hopefully not the computers that run the fuel injection and ignition, though.

The specs say no less than 6volts. In the real world when the temperature drops down to -70F or colder and batteries get old the voltage goes well below that: deal with it.