Pls help with a battery sizing question. I'm powering simple stuff - nav lights, bilge, undergunnel lights, etc - no big stereo or TM. I'd like the smallest battery possible for weight considerations. My motor doesn't have the alternator capability so I need the juice to last for a night's worth of fishing. I was thinking the agm Odyssey batteries for durability/weight. Thought the pc680 was about the right size (and a nice alum hold down bracket is available). Thoughts? Thks.