AC to DC Converter

Yes, get some batteries. Store them charged.

batteries large enough limit it to lead acid, which have a finite life with declining poer over time, shouldnt be stored discharged and they go dead just sitting around and after such discharge dont recover their previous capacity......

probably better off with a 12 volt generator.

you could buy a large battery charger and try it in use. if its not good enough return to store.

my 200 amp boost says it supplies 60 amps at 12

Someone had the best idea. Just jump from your car battery if necessary.

Generators can also deteriorate if not run regularly, and cost more than batteries.

That can also have a couple of downsides, though --

if you're not careful, you can discharge your car battery and strand yourself

it's not always possible to move a car into a suitable position to use it that way

Maybe one could use the BOAT's battery (if it has one)?