Re: maintance free battery or not
NOT maintenance free.
Newer boats typically have high output alternators and charge batteries very quickly. Even though voltage regulated, the battery may need to vent given the current being used to charge it. When it vents, you lose water, even with maintenance-free batteries (yes, they still have a vent in them). If it's maintenance free, there is no way to replace any water that is lost, so the battery will die a premature death.
Older outboards (in particular) did not have voltage regulators and would often charge a battery up to just beyond 16 VDC while underway. The result, again, may be venting and the subsequent need to replace water periodically or suffer premature battery death.