That risk could be minimized by installing multiple small banks separated in space, rather that a few larger banks. ... You can't stop [a battery fire] once it starts. That battery has to discharge.

With a bit of planning ahead, those multiple small banks might be able to be jettisoned overboard if they are on fire. Or keep them in small, below waterline compartments that can be easily flooded in case of fire.

Thinking like a practical environmentalist, I don't think electric propulsion in port is really feasible. Not without a big engine generating the electricity, which sort of defeats the purpose. Probably much more practical to require cleaner engines while in/near ports. Perhaps better quality fuel (bunker fuel is pretty nasty stuff). Maybe in combination with some rudimentary exhaust treatment - which can be bypassed when out of port. Or just bite the bullet and go to a better quality fuel all of the time. The contribution to environmental damage is the same whether the ship is in port or at sea. We just notice it more when they're in port.

--Peter