"Marine batteries" I assume you mean deep cycle? If that is the case they are just meant to be drawn down to 50-60% repeatedly with out harm to the plates. They usually take longer to charge because they have been drawn down so low. Normal car batteries are meant for a quick draw down and quick recharge.
For your needs don't waste your money on the "marine" battery just get a battery tender for cheap or a battery switch. Or just plain disconnect it it takes what 5 minutes? Unless your worried about resetting your presets and what not?