These Kisae Inverter/Chargers can be configured in several different ways. The manual I have describes four of them but there are actually 6 different ways my unit will operate. The default (in1) for these units is to automatically supply 120v power from the house bank the instant shore power is removed for any reason. I have mine configured (In5) so that if the shore power dies, (likely during the winter months here) the inverter will NOT supply 120v power from the house bank batteries. I have it set this way so that if the shore power dies, my two space warmers and the dehumidifier won't keep running and destroy my house bank. The unit is supposed to shut down (and alarm) if the house bank falls below a certain level but by then it may be too late. Now, when I'm on the water and want 120v power I just turn the inverter on. Back on the dock just plug the shore power back in and you're good to go. The in5 setting allows the unit to pass the 120v shore power straight through whether it is "on" or not.