Pull the cover off the ITOA and look inside. I looked inside mine last week and also checked cable screw tightness. Mine was fine, but most of the problems many have had with this ATS are evident when you pull the cover. The box itself is plastic and readily shows overheating. I would also check tightness of the internal connections (with no power applied of course).
Also, did this issue start immediately after the battery installation or some other system change? Curious as I have the same year coach and same ATS and would be very interested on what you find and your resolution. The two ATS units I am considering are the Progressive Dynamics PD52DCS or Esco LPT50BRD noting that Newmar now installs the Progressive Dynamics PD52 in new coaches. Some of the replacement consideration is the wiring. I found that some boxes won't work due to current wire installation locations and length vs. what is required for a new box due to the cable installation location within the box and the need to increase wire length.
2015 Tiffin Phaeton 40QBH
2018 Chevrolet Colorado Toad
Roadmaster Tow Setup