Slight correction on my comment regarding some inverters having voltage monitors.....should have said that they would show coach battery voltage not chassis battery voltage.
Regarding the fully charged coach and chassis battery not operating loads.......my first thought was use/store not on (as JamieGeek first suggested). The other thing I thought is how do you know the batteries are fully charged......measured 12.6 + volts with a meter? When the use/store or disconnect switches for coach and chassis battery latching relays are operated you should hear the clunk of the particular relay(s) operating (closing or releasing). If you do not hear the clunk......there is something wrong with the latching relay(s) or the wiring that enables the operation of the latching relays. Also when operating the emergency interconnect switch you should hear the battery interconnect relay operate. I am not familiar with the BIM operation.
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