I have read bits and pieces (posts) indicating that the Q7 somehow limits the amount of power that can be sent to the trailer (via Aux pin #4 of the towing connector).
Is there any truth to it?
If limited, what IS the limit (amps)?
If limited, HOW does it limit the flow?

It is a MUST for me to charge the trailer (house) batteries while driving. If need be, i have to modify the factory setup, or ADD a fused circuit (simply speaking, run a phat wire from the car power panel (probably best to use switched power) directly to pin 4.

https://i.pinimg.com/736x/c6/2d/4e/c...51144e4057.jpg
https://www.etrailer.com/static/imag...r%20Coded2.jpg

 

I would expect that if you want to charge large batteries, such as those in a travel trailer, you would need either a "phat" connection, as you described it, or other means such as solar. The 12V connection in the seven pin would be a very slow method for charging full-sized batteries, indeed! It works fine for charging the small emergency brake battery or the trailer electric brakes, which are its purpose.

 

I don't believe the charge wire out of the module is very thick indicating you not gonna charge at 50 amps. If it were me, I would take a heavier wire off the car battery and run it to the rear near the module. Use the charge wire out of the module as the trigger for a relay with the cars battery wire you just ran. Then solder or attach the heavy wire to the hitch's connection point. You can buy starter solenoids cheaply enough to use as a relay or use a ready made relay.

 

I have owned a number of trailers, campervans and Class C RV's and here is the deal with charging house batteries. Unlike a Camper van or class C RV where the alternator is heavy duty to charge both batteries, the wires are larger to accommodate charging of house batteries and the wire runs are short, a trailer's battery is a long distance from the engine alternator and battery, plus the wiring to and in the 7-pin connector in the tow vehicle is whimpy. Therefore you get very little current back to the battery when towing a trailer and it is likely that cars with trailer hitches limit the amount of current to the 7-pin connector. The proper way to charge a trailer battery from a tow vehicle is to install a DC to DC charger in the TV and run a decent sized wire (like an AWG 8) from the tow vehicle battery to the trailer battery with a good quality connector like an Anderson Connector near the trailer hitch. Another thing to address is to make sure the connection is broken with a relay when the tow vehicle is not running or unplug the 7-pin connector whenever you stop for the night! Otherwise you may be stranded out in the boondocks in some beautiful secluded camp spot where you have just spend several days before finding a dead battery when starting the TV to depart. You can check that easily with a voltmeter reading with the car running and not running. It might just be easier to install solar on the trailer and forget trying to charge from the tow vehicle. Solar will charge when you are traveling and when you are camping so it seems like a better investment of both money and effort!

 

I don't know about the power being limited, but I do know that my 2019 Q7 did not supply sufficient voltage for my travel trailer camera to function. My 2015 Q7 did not have this issue. I use the below adapter to modify the voltage and it works fine. It also makes my utility trailer lights function correctly:

7-Way Vehicle Power Adapter for Furrion RV Observation Camera
https://www.etrailer.com/tracking.as...ode=20715-2122

 

So it looks like no one knows
a) how the Q7 LIMITS the amps (I am not aware of an 'amp limiting' device)?
b) what this limit is.

To get around the 'charging limitation': where is a convenient (easily accessible, rear of car) high amp circuit to misuse (= to splice into, if rarely used). Think 'subwoofer amp' or 'rear windshield defroster' or 'rear heated seats' or 'rear cigarette lighter'.