Luckily this is not true, otherwise the adoption of EV’s would not be spreading the way it is. In our Vision Marine boats for example, the 48v batteries are rated for an 80% capacity at 3000 charge cycles or 20-30 years of average use. If a rental company was to use a boat 8 hours per day for 300 days/year that would take 10 years to to reach a 20% degradation on the battery.  Keep in mind, that is still a fully functional battery, just with less range. Combined with minimal moving parts, EBoats have a much lower failure rate and therefore a lower maintenance cost  than high mileage gas boat engines. The average battery will last 2,000-4,000+ charge cycles or 8-16 years of above average use. There are many EV batteries that have hundreds of thousands of miles on them. This Guinness record holder averaged ~300,000 miles per battery.