As I understand, one should press the "store" to disconnect the batteries from the electrical system.
I have observed on my AS, that if I press "store" when plugged into shore power the red indicator on this panel with remain lit. I am sure this is an indication the converter is supplying voltage to the system, even without the batteries connected.
I know the "system status indicator” uses only voltage to determine the red, yellow or green status of the batteries. Remember this is a rather poor indicator of true battery status. I believe you are seeing a higher indication with the master switch in the "store" position because the batteries are in a discharged state, and when you place the master switch in the "use" position and the batteries are in the circuit, they are pulling down the voltage to a point the status indicator sees less voltage. I would allow the batteries to charge overnight and test this theory.
The short answer would have been, place the switch in the "store" position when the trailer is not in use.
Jeff & Cindy
'09 27FB Flying Cloud
'91 350 LE MH