The charging circuit in the converter is current limited. No matter how many batteries are connected to it, it will only put out as much current as it is designed for. You are better off keeping them all connected together. Otherwise, you will end up with some charged to a higher voltage. When you then reconnect them, the higher voltage ones will begin to discharge into the lower voltage ones.
2011 Silverado 2500HD Duramax, 4x4, crew cab, long bed
Palomino Puma 253-FBS, 27' 5th wheel
1994 19' Class B on Chevy chassis