Solar power is a natural fit for many boat applications, from small to large. A trailerable boat can use a small solar module like the FlexPower 10, which can be tied or bungee cord attached to the mainsail cover, and then stowed under a bunk or cushion, or rolled up into a cylinder for storage. Or the lightweight fiberglass-backed Innergy 10 watt solar module that can be glued down and walked on. Either will keep the battery charged, and prevent sulfation, so the next time you use the boat, the battery will be ready.