Black to positive (like home wiring, black is "hot") and white to ground (no neutral on battery systems, so white is ground).
They are easy to get confused on, most battery devices use red for "hot" and black for "ground". RV "house" (notice the term "house") batteries use the same color coding as your "house"...black is hot and white is neutral/ground for the system. If the battery weren't connected to your RV "house", it would, by convention be red for hot and black for ground. Since they are your "house" batteries, they take the house color codes.
BTW, noticed your other post, and, Welcome to the FunFinder community!! Great bunch of folks (well there used to be a couple of soreheads, but, haven't heard much from them lately...) and you, of course, are more than welcome to "pick our brains"; that's what we're all here for...sharing knowledge, modifications and experiences. The day I don't have anything else to learn would be a sad day indeed and one that I hope never comes! Again, Welcome!