Excellent post! You rock with real world basic engineering knowledge. The power required to charge an EV is based on Horse Power, as you correctly point out. It is NOT voltage or amps by themselves.
It is always voltage times amps, in this case 746 watts equals 1 horsepower.
746 watts is the product of voltage time amperage and it can happen many ways. 373 volts time 2 amps equals 746 watts or 1 hp. 2 volts times 373 amps also equals 746 watts as would any combination.
The punch line, if you will, is that all of this is determined by the internal resistance of the battery.