I'm an ex bass fisherman, so boats and electronics I'm ok with. Our family just bought a 2005 sea ray 220 select that I want to ad a sub woofer and amps to. The boat was manufactured only with 1 battery. I need to add an extra battery I understand. My question is: I have 2 good optima Dm31 dual purpose batteries an on board smart charger and a Lowrance hds9 left over from my bass boat days. Can I mount the 2 optima's , mount the charger and hds unit and just use them to supply power to my sub amp and mapping unit? I realize I will have to plug the boat in to charge those batteries when not in use but can it be done or am I thinking wrong? The 2 batteries would get me two solid days on the trolling motor and running 3 fish finer units no problems. Will a sub amp draw way more power? thoughts and advise please!! and Thank you in advance for helping out a newbie!!