Hi Land-Yacht welcome to the forum. I'm assuming the low voltage alarm is for the coach batteries. Is the coach plugged in to shore power? has that problem come back, or are you now only having problems with the starter battery draining?
You stated everything electrical seems to be working fine. Are you referring to the charger and such, or are you referring to things like the interior lights and fans? If the charger or inverter, what component did you test and how was it tested and what were the readings if any?
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2001 Suburban 4x4. 6.0L, 4.10 3/4 ton **** 2005 Jayco Jay Flight 27BH **** 1986 Coleman Columbia Popup