Battery Cable Size

[captaintodd]

I am planning to move the battery for my Evinrude 115 etec. The battery will be about 15' from the engine, and I plan to need 20 feet of battery cable. Does anyone know the required cable size for this type of length? I realize there will be voltage drop, but do not know what the formula is to figure that?

[boats.net]

With that kind of distance, I do not recommend anything smaller than a 4awg.