Finally buying a strong inverter. How many batteries to buy?

People have just given various ideas because there are many ways to accomplish how we power our RV's. We aren't the ones who would talk you out of anything, physics and the available technology does that, we just try to explain what your options are. I call it an energy management plan and we all have one no matter if it's a wool hat and long johns in a tent or a $800,00 DP. Air conditioning is usually the biggest glitch.