I’m sure your correct on the DC to DC charger but again you have solar on the roof charging your batteries along with the car charging so unless it is raining and very cloudy you won’t need it. My batteries are always fully charged with the solar. I would spend my money on more solar panels and a MPPT controller and I did. Have fun with your Black Series trailer.Thanks for the reply. Glad to hear they did not delete the Anderson plug. That will save me the time of having to install one on the trailer.
You might want to check out the advantages to running a DC-DC charger, as well as the limitations you may run into charging from the small wire in the vehicle's 7 pin connector.
The main benefit I see with the DC-DC charger is DC-DC charger's ability to control the input voltage from the alternator to charge the auxiliary batteries to 100%. The DC-DC charger also uses software to apply the correct charging profile for the battery type and the battery's current state of charge.
In my opinion, there are numerous advantages to running a DC-DC charger whether you run AGM, lead acid, or Lithium Ion. I don't believe DC-DC chargers are only needed for Lithium Ion batteries.
Here's a couple links that have some relevant information regarding DC-Dc chargers:
REDARC BCDC and SBI Explained
There is a lot of "Talk" about DC to DC chargers and "Do i really need it" questions about this subject.
What is a REDARC BCDC and what does it do? (although this is a manufacture's video, it goes into how DC-DC chargers work and why they may be advantageous.)
Again, thanks for the information.