sch911 wrote:
If I read your description correctly it sounds like possible bad house batteries.
That was my first thought also.
But, if I re-read, I see some inconsistencies.
Might be interesting for the OP to start the genset, the way the "beep beep" thing happens while someone monitors the voltage right at the coach battery terminals.
With no prior voltage measurement to use as a baseline it is hard to say what is going on.
OP, I'd try your start with the genset, the way you did as described in this post. THEN, after the start attempt, check the battery voltage.
If the battery voltage is still about 12.7, then you probably have a connection issue.
If the battery is lower then about 12.2, then you probably have bad batteries.
Hope this helps.