Battery packs degrade so fast with constant use. They would replace it every year if not every month.

Nonsense; they are good for many thousands of cycles which generally translates into many years of continuous use. Mostly batteries degrade on a very predictable scale as well and very gradually.

All of this is well known and anticipated by companies that deploy batteries in ferries, and other short range boats. It's just economics. You have energy savings and a battery that is good for a given number of cycles and engine hours. Either that adds up or it doesn't. Basically, it will be years before you need to service them and you can just use math to calculate whether that's economic or not.

Apparently it does. That's why the use of batteries in short range nautical applications is booming. You have some range constraints but anyone operating within those constraints is looking at switching over already. Battery longevity is not the concern here generally.