carbon monoxide/propane alarm

Typical life for CO detector is about 7 years from date of manufacture, so possible but not likely it is at end-of-life. More likely low voltage reset time, but that is usually not more than a few minutes in my experience. But then I disconnect my battery to keep it from going flat in storage. So maybe a flat battery would cause it to alarm while the converter was trying to get the battery charged.

But whatever the cause, you need to get it resolved. That alarm is a true life saver, don't just remove/disconnect it. Your life (and that of your entire family) depend on it.