You’d need to use silver plated copper buss bar as conductors, 150kW @ 48VDC is 3125 Amps. I’m not familiar with DC ampacity tables, but you’d need (9) 3” conduits each containing (3) #500 MCM conductors for a three-phase 3125A alternating current circuit. One foot of #500MCM copper weighs 1.5 lbs, so each foot would have 27 times 1.5 lbs or 40.5 lbs per foot.
150kW @ 400V is 375A, a single set of #500MCM can carry the current, 4.5 lbs per foot.
The risk of being shocked by 400VDC while using the car is essentially 0, so they use higher voltage to save on conductor material.
There’s no way in hell I’d ever open up an EV battery myself and I know enough to do it safely. DC is incredibly scary, make sure to discharge your start/run caps if you replace them yourself!