The early NVIDIA drive based “fully autonomous concept cars” had like 2-3kw worth of computing, Drive Pegasus which is still probably is not enough for L4/5 is 500W per unit and it seems like the minimum viable configuration is 2 of them in a vehicle.

It still isn’t a lot compared to moving the car but it is quite a bit of power.

For a car with 100kw/h battery pack and a range of 500km a 1kw driving computer would reduce the range by about 5% which is about as much as having the air conditioner on.