Together and Alone: Economic Viability of Batteries Powering the Western Mediterranean Cruise Corridor

Batteries can power a large ship two ways: carried together onboard, or sent alone as speculative battery vessels (BVs) coupled to a host under way, powering it over a short segment, and recharging in port. Onboard storage is limited by heterogeneous charging opportunities; a BV is more flexible but carries high fixed costs. We assess both on the busy Western Mediterranean cruise corridor, subject to EU policy on port couplers (OPS) and emissions, using real schedules, prices and sea states to optimise pack sizes, charging times and BV routes for maximum fleet profit. At projected 2040 battery costs, onboard batteries are viable first, led in value order by the near-year-round hosts that exploit sunk OPS spare capacity, from an implied carbon price around EUR 95/tCO2e. BVs switch on above about EUR 175/tCO2e, below the implied all-in carbon price of about EUR 260/tCO2e from the current regulatory stack. Four BVs supplementing onboard packs then electrify about 50% of the fleet's at-sea energy against 36% without them, by serving hosts that leave the corridor seasonally and raising port-coupler utilisation. High BV utilisation requires traffic density or host route flexibility.