Can two 6V and one 12V be charged by rv system?

I did thjs once...you will suck down the bank faster than if they are seperate. Yes you can charge together but the 12 will pull down nearly twic as fast as the sixes and most of the power of the sixes will go into topping up the twelve. I dont knkw or care what the theory is here, in my case i bet the bank lost about a third of its run time.