question

The input voltage is lower on the second picture. The orion regulates the charging power to keep the input voltage above the shutdown voltage (13.1V).
Are you using the original audi cabling to feed the Orion?
Theres also a temperature warning and a fault listed in the manual, but im not sure if the device starts to derate before theres a notification

Thanks, I could try lowering the shutdown voltage, but it appears to be not shutting down. The cabling is the trailer umbilical cord which is 10AWG.

But the Orion is located in the trailer? So you got long, relatively thin cabling, with a trailer plug in the mix as well. All factors that drive the wire resistance up, leading to higher losses. You can for some degree compensate for that trough settings, but ultimately its turning the cabling into a heating element.

I can only assume the total cable length involved. According to the wiring unlimited handbook of victron, for a total of 16m (thats 8m of positive and 8m of negative cable) at 16A, they recommend a 16mm2, thats AWG5. I guess AWG5 is only theoretical (is not being produced), so in reality it would need to be be AWG4

Yes, Orion is in the trailer. Yes, possible the wire gauge is too small, but it looks like 10AWG will handle 15A up to 6m or so. It's hard to say what the distance is. Since it's fused at 15A I would guess that's what Audi thought it could handle. In any case, maybe there's some voltage drop but I'd expect more current and initially this is the case.

I have battled performance issues with my older Orion 12/12-18 and it is very hard to nail down the root cause. I feel like there are many possible contributing factors and your best bet is to address them all individually and see if any performance increase occurs.

In my case, I have determined that the most likely cause of my issues is the derating when the device gets warm. I understand the Orion XS is more efficient than the older ones so hopefully that's not the problem but I would check the ambient temp of the location in which the XS is intalled to see if it's getting warm in there. That might explain why it gets worse over time, like with mine.

Next I would consider a dedicated, thicker cable from the Audi to the trailer. I run 6awg from the starter battery to an anderson plug at the tow bar, then it's also 6awg from there to the DCDC charger. This should result in pretty minimal voltage drop, which will improve your chances of getting good performance. I have a basic alternator so am not personally familiar with how smart alternators behave in the real world but I would expect it to be the same in that you want as little voltage drop as possible.

I am curious how you got the XS working in a camper. I have been holding off for an isolated version because I thought you needed that when there wasn't a common ground, as per in a trailer. Wonder if that has anything to do with it.