The 'use/store' switch operates a 12VDC solenoid that will disconnect your battery bank from the trailer's 12VDC electrical system AND converter/charger when in the 'store' position. If you are connected to shore power, the indicator light at the switch is on regardless of it's position, requiring you to SET the switch at the desired position BEFORE you plug in.
If you will be storing the rig with power available, you should position the switch to 'USE' so that the batteries will be receiving the charge voltage from the converter...........A WORD OF WARNING HERE...........if you have the stock converter, leaving it connected to your batteries will quickly burn out the batteries as it is a single stage charger, not a 'smart' 3-stage unit.
There are numerous threads dealing with this topic, which you should checks out. You can also PM me if you have any other questions. There are also other options available for battery storage and maintenance.
Lew Farber...RVIA Certified Master Tech...ABYC Certified Master Marine Electrician
SOLAR TECH ENERGY SYSTEMS, INC.
AM SOLAR ...MAGNUM…VICTRON ENERGY...LITHIUM & LIFELINE BATTERIES…MARINE REFRIGERATION