Cascadia + Tripac + Xantrax Fleetpower problem

I recently bought a 2011 Freightliner Cascadia SLP125 with high roof, Xantrex FleetPower FP1000 inverter, Tripac APU and the four standard Freightliner starter batteries (no extra bank is installed).

My problem is that the Tripac (although it works, cools and heats) it does not charge the truck batteries when it runs. Is it not supposed to do that?

There is an amber light on the instrument console saying ”120V” that comes on when the inverter is on. No mechanics that I talked to recognizes this light, my guess is they installed it when they installed the Tripac. This concerns me since amber is a warning color on the instrument cluster.

What I tried:

I have changed batteries and the Tripac alternator.

I have inspected the 50A megafuse.

My aux powernet distribution module has a firm red LED telling me it works ok.

The inverter 120V outlets work when the truck engine runs and for as long as the batteries last.

I tried the Sense pin on the Tripac controller fusebox (under the bunk), which is the pin that is telling the controller that the alternator is producing electricity, and there is 0V now (weird because there was 12V coming there the last time I tested). Guess next step is to follow that cable…

Recently I learned from the Xantrex manual that you should not use the inverter with starter batteries that are measured in CCA, you need RV batteries that are measured in Ah. Hope this might help someone.

Any ideas along the way..? Thanks in advance!