My CO detector also beeps when batteries get discharged. A visitor had flipped on the compartment lights and we were using the heater. About 3 AM i woke up to a quiet beeping of the CO detector and heard the furnace fan just barely turning. I had to get up and run the generator for an hour or two to get through the night. Now the compartment lights have an indicator light on the dash!
Those adaptors for 50-30 or 30-20 are available at most Walmarts, no need to go to an RV store.
Bob & Donna
'98 Gulf Stream Sun Voyager DP being pushed by a '00 Beetle TDI