Yea, they only use 150-200 kWh per day, that's not a lot of batteries to store on a large ship like that (it's like ~5-10 EVs worth of batteries maybe? not the whole car, just the batteries!), even if you couldn't charge between sailings (which you could). I think it was probably a cost thing, too, as this system with a cable is probably way cheaper than batteries.

edit: I was trying to reinforce here that, although this application could easily have used batteries due to the low energy needed per day, it didn't because there was a better solution due to the pre-existing cable infrastructure. Certainly this cable method isn't useful for most ferries, and most ferries will be traveling further and faster and require way more batteries.