batteries
What are you asking for in length of time, power consumpsion or static siting in the boat with no draw on the batteries. Batteries in series will give you more voltage, but you neet to be careful that you do not place 24 volts on 12 volt equipment. Series would give you more usage time for a given number of pieces of equipment. I would think that if you have a lot of equipment on your boat that you would need to have batteries in parralel. The more equipment the more batteries in parrallel you would need to feed current to the different pieces of equipment. you would also need to check the guage of the wirement in your boat, more current the larger the wire needs to be.If you are looking for batteries to last a long time in a static state, good luck some batteries will last a long time with good maintenance, water level and keeping them clean of corrosion etc. fair winds AL