If you want to spend money look at the Sterling battery to battery chargers I fitted one to a van for someone once nice bits of kit. He also had me fit a fuel cell generator to it talk about money no object https://sterling-power.com/products/battery-to-battery-chargers https://www.efoy.com/
I've been looking at them and trying to justify one for about as long haha. In the end I went for the multi component set up simply because it was a bit cheaper. As you know I've got big cables on everything anyway but I do like the idea of a more efficient use of the alternator and the fact you could hang a gel or agm battery off the other end of it, whilst keeping a flooded lead acid for the starter. Now I just need to convince myself that the Smartpass 120 is a necessary partner
The Sterling Digital alternator charge controller helps the batteries on my boat. It turns the alternator into a 4 stage battery charger. And it only cost £100.. Trouble is on my 7HP 330cc Yanmar diesel, it drops the idle speed towards zero on a cold engine and makes it hard to get the engine in gear without stalling it.