If you had the converter turned off, then you were not charging the battery and the CO/Propane detector and other items were using 12V power. This will drain the battery and cause a low voltage alarm. Over time, it will damage the battery. Once you turn on the converter is turned on, it supplies 12V to the system and the alarm will shut off. Not sure why you would need to turn off breakers when plugged in to shore power.
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