How much time away from a power grid are you expecting to have? Two ways to approach the issue you face and one is obviously picking up a small inverter generator. Those are the quiet ones. I have a 2000w Champion and yes, it is quiet. You can have a normal conversation with another person just a few feet away when it’s running. It’ll charge boat batteries and plus something like that is handy to have.
Another solution might be to look at 12v alternators for your boat’s electrical system. I put one on my boat a few years ago and it’s been great. I’ll top my batteries off throughout the winter but when my boat is running the alternator tops off my trolling motor batteries. As soon as the main motor is fired up and the starting/accessory battery is brought back up excess amps are diverted to my 24v system. Since I’ve installed that thing Ive rarely had to plug my three bank charger in.