What's more scarce is the factory capacity to build the batteries, and the scale of their supply chains. But even that is expanding by 10x every five years. We are currently building more than a TWh per year of batteries.

If there is demand for batteries in ships, it is going to be far smaller than for cars, which is currently 80% of battery demand (the rest is mostly grid storage). So ship batteries will at most slow the fall of battery pricing by a small amount.