Need Help with boat audio system

by Rick Bailey
(New York State )

Hello im trying to figure out i have and old 70s series evinrude motor and im trying to see if there is an alternator or something on the engine that charges the battery. I would like to put in two main speakers and a subwoofer and amp and cd player but im not sure how i would keep my elec start battery charged up and if i would need a secondary battery for the cd player and amp and such and how i would keep them both charged up.So i would greatly appreciate someones help if they could help me out im not planing to run a large amount of watts and a big system just two main speakers and a subwoofer just for some music and bass while out in the boat. I read online else where u can get a generator for the boat or there are boat alternators but my engine is old so idk how i would go about doing it but im sure theres some way out there that would do what im looking for im not trying to spend outrageous amouints of money just to do so but please help me out thanks Rick.