Battery disconnects are installed for storage, not for disconnecting while using the RV. IF you store with 120 available, you do NOT disconnect. If you have an Inverter/Charger, the battery disconnect will NOT disconnect the battery cable from the Inverter. A LOT of RV's with just Converters will have them connected to the coach batteries even if the battery disconnect is OFF and you are connected to Shore Power. The RV's that have the Power Converter connected on the USE side of the battery disconnect solenoid will then allow the coach batteries to go DEAD in 2 or 3 weeks if the Disconnect is OFF. The reason is, they usually connect the LP/CO detectors direct on the battery side to prevent voltage spikes causing false alarms. But to answer your question---NO, there is NO good reason to turn your batteries OFF when connected to 120 shore power or using the RV. Doug