Tugboats are a perfect use for battery electric boats! Most tugs work close to a port, they don't need to travel very far, need to be extraordinarily powerful for their size, and they need to change power output rapidly to manoeuvre a ship.

A harbour tug internally is almost entirely engine. Well, two engines, because an engine failure during tug operations is almost always disastrous.

Not to mention that many of them are diesel-electric hybrid already, going back to the 1940's.