If the ferry uses 150-200 kWh/day, that's two Tesla batteries assuming no recharging during the day (so realistically, you could run it on one, since the ferry presumably isn't constantly moving).

Of course, the fixed cable avoids having to replace the battery every couple years, might be lighter/cheaper etc. - but it could absolutely be implemented using batteries.

(This assumes the numbers are accurate, the 100 liters of fuel vs. only needing 200 kWh seems odd.)