Lance, I think your concerns about DC-DC charging are valid. I just installed the Battle Born batteries last week, so I have limited observations on how it is working. The Battle Borns ship with a 100% SOC, so I have not seen what happens with alternator charging at a low SOC. So far, all I've done is turn on my inverter and run a number of items to create a load on the batteries, then start the vehicle. I monitored the load with my Victron SmartShunt as a 12amp draw and I think I recall the battery voltage drop to 13.1v. When the alternator kicked in, I saw a 6amp charge which nets out at an 18amp charge rate, so not a concern.
Again, both the factory and Battle Born told me a DC-DC charger isn't necessary. Perhaps they assume the battery should never drop in voltage enough to be a concern, because of my solar, generator, wire resistance or whatever, I'm not sure. In any case, I'm still considering a DC-DC charger for the reasons you mentioned. I looked under the hood and figuring out the wiring for the charger will be a bit of a challenge for me.
"2 Frazzled", I haven't even camped with my new 2552 yet, but so far, I haven't seen the inverter turn on, unless I manually turn it on.
On a side note, I bought a Bluetti AC200 Max portable power station. It has LiFePO4 batteries like the Battle Borns, 2048Wh capacity, and a 2200W pure sine wave inverter. It even has a 30amp RV plug. If my microwave isn't on an inverted outlet, I can just plug it in to the Bluetti (I bought a 6' 20amp extension cord). The Bluetti costs not much more than 2 Battle Borns and doubles my capacity. Of course, it takes up some space, but I think I'm going to like having it with all the outlets, inverter, and convenient wireless phone charging. I bought a portable solar panel to keep it charged, and this might come in handy if I'm parked in the shade - I can move my portable panel to the sun and keep charging the Bluetti.
