Just thinking out loud here, but if the main problem with building 2.5 billion EVs is making the batteries, why would that change anything if those 90,000 cargo ships each need 56,000 EV's worth of batteries? I'm sure there's some efficiency to be gained by making larger batteries, but it still doesn't quite add up.

Of course this also assuming a cargo ship is as efficient as a car in terms of replacing the ICE with an electric motor. I've heard the fuel these cargo ships use is some of the worst quality fuel that we have and it doesn't burn well, but it's very cheap in the insane quantities they need.