Center Console Boats And More

How can I put my home stereo on a pontoon boat running on a car battery?

It's my dad's boat, and he doesn't want a big sound system installed (and I don't want to pay for that anyway) but we have a boat parade, and I want to run my home stereo from the boat. Is this possible? What if I can get my hands on another car battery? could one car battery, (not the battery for the boat) run the stereo? How would I go about hooking this up?
I was thinking about a converter or something... do you think it would basically cut out if I turned it up very loud though? I'm thinking it would...