I have my solution to the noted expansion issues. I have 3 x AC180s and 2 x AC70s. I also have the charger 1, not installed in my vehicle. I also have a spare 100Ah LFP deep cycle battery.
I plug the charger 1 into the AC180 solar input port and power it from the 100Ah LFP. This gets me over 500W of charge and slightly more than double the AC180s capacity. Or, 1152Wh from the AC180 + approx 1,300Wh from the 100Ah.
I don’t need to worry about charging the 100Ah as I also have a Victron Smart charger for grid charging, or solar, or genny. I bought my second AC70 with the C1 as a combo on sale, which if worked out this way got me the charger 1 for under $100 AUD. I made up a shorter input cable for the C1 to do this.
Due to the C1’s variable voltage, it will work from most deep cycle batteries and charge most small to mid range power stations.