Question: how many watts does it take to start a car?
Answer: Watts are Volts x Amps so say you need 2400 watts to crank a car engine (about the same as an electric kettle) - then you could theoretically have that as 12v x 200 amps (2.4kW) or 120v x 20 amps (same 2.4kW) or even 240v x 10 amps (still 2.4kW) - but asking how many volts without knowing the current (amps) is ...