Originally Posted by camlivy
Maybe not just surges--we have camped with shore power to break camp in the morning with low batteries, an indication to me that the shore power wasn't working or at least not properly. Despite the "light" being on next to the plug.
Or it could mean that your inverter/charger wasn't turned on. Pedantic explanation ahead— you have been warned!
Just plugging into shore power doesn't charge the batteries; without the inverter/charger turning that 120vAC shore power into 12vDC power, all of your 12v
appliances and lights were draining the house batteries rather than working from shore power, and none of the shore power was going into the batteries.
I don't know if that can happen with the Magnum inverter/charger, but it is
possible with the TrippLite inverter/charger, which has a three-position switch on the front of the unit (Auto/invert, off, charge only). The three-position switch can be in "auto/invert" and the unit will detect the incoming 120vAC power and convert it to 12vDC power, and switch back to "Invert" mode when the shore power is gone. If the unit is in "Charge only" mode the inverter/charger will detect the incoming 120vAC power and convert it to 12vDC, but will not switch back to "Invert" mode when the shore power is gone. But if the unit is "Off" then it just sits there, and the 12vDC side is completely isolated from the 120vAC side.
—End pedantic explanation.
I've made the mistake of leaving the inverter in the "Off" position by accident (once) and it did exactly what you describe. Shore power working, but batteries discharging.