Re: Differences ???
Not a whole lot. Expensive marine batteries are in general heavier duty, with thicker lead plates to resist all the vibrations that come from being in a boat. Cheap marine batteries are the same as regular automotive batteries - except they have a different label and a bigger price tag. My boat has had a $29.99 store brand car battery in it for the last nine years, still works great.
Mostly, the only thing you need to be concerned with when buying a boat battery is cranking vs deep cycle and quality vs cheap crap. Whether it says marine or not doesn't really matter.
