I would think this can only ever be useful in places where a connection is needed only for a short time, e.g. to compensate the loss of a connection. Not only are battery tankers a huge investment, they also have an extremely short lifespan.
According to the article, their batteries have a lifespan of 6000 cycles and a capacity of 241MWh. That means that during it's lifetime, one ship can transport 1446000MWh of energy.
According to this study (https://www.sciencedirect.com/science/article/pii/S258900422...), it costs 41.5$ to transport 1MWh 1000 miles across high voltage dc lines (including initial investment). That would be 10,000$ for a 1000mile trip for this ship. I believe there might be some edge cases where it is absolutely impossible to build cables or the link is only needed for very short timespans but other than that I don't see this become profitable.
According to this study (https://www.sciencedirect.com/science/article/pii/S258900422...), it costs 41.5$ to transport 1MWh 1000 miles across high voltage dc lines (including initial investment). That would be 10,000$ for a 1000mile trip for this ship. I believe there might be some edge cases where it is absolutely impossible to build cables or the link is only needed for very short timespans but other than that I don't see this become profitable.