dc - dc charger

Our current T5 has a Sargent EC155 that takes care of things but I don't like it. So for our T6 I will use a Victron 12/10 charger and Merlin Smartgauge from @travelvolts and either up rate or double the battery. Currently if I have the leisure power (230V & 12V) switched on at the master it...

there's a thick cable under the passenger seat that I'm wondering what it is. It has a barcode on it? so it looks original. I'm fitting a leisure battery /ctek solar charger - so am hoping it could be useful. Guy