Do I need a DC to DC charger?

[fantasque]

I have a 2014 T5.1 SE with one of Roger’s excellent 200 watt Solar kits with the Victron Solar Charger connected to the rear leisure battery. When parked up at home this easily keeps the leisure batteries fully charged in float mode. I would ideally like this setup to keep the start battery fully charged as well. I am aware of the new Dometic Solar Charger which would do the job but is there another way? Would a Victron DC to DC charger work? Is it possible to configure it to take any excess power from the leisure battery to charge the start battery?
As you can probably tell, I am not too technical so please be gentle with me.

 

[dspuk]

As you likely have found out, Victron don’t do a unit that trickles the Starter, shame because the BT app was great. There is a thread on another chat about trickles and the recent unit Roger has that improves on the 1A I get with mine, the Dometic you mention. My original setup had the Victron but I had to change to an ePever and thread a wire down to the relay. I looked at Victron work arounds but they were more faff, more space, more cost and more complex.