Please could you give me some advice. I am replacing a Trumar PMW with a Victrom MPPT 100 I 20 solar charger. But my old charger also charged the starter battery. Can I connect the Orion-Tr Smart 12/12V 18A to the Load terminals to trickle-charge the starter battery in that direction, or do I have to wire the MPPT to the starter battery and then the Orion 12v/12v charges the leisure batteries? I’d prefer the first option but not sure if alternator or mains charger have any effect on this setup. Thanks. Mark.
I can’t see either scenario you suggest working reliably.
There was a similar thread recently here where an Orion was used to trickle charge a starter battery, but this resulted in a charging loop;
The OP resolved the issue by installing a separate battery maintainer.
Maybe that would work for you?
Depends on the battery chemistries being used. If both are lead acid, then the simplest would be to use a cyrix coupler between starter and leisure battery. It then doesnt matter anymore which battery receives a charge, and from which source. As soon as one gets charged the cyrix will close and thus both batteries get charged.
But if you use LFP on the leisure side then a cyrix would not be optimal due to different charge requirements. In that case i would connect all charging sources to the starter battery, and then use an orion to charge the leisure battery.
Of course it also depends on the system size. Charging a 300Ah LFP by going “through” a 65Ah starter could be a challenge. So you could also think about splitting the PV, for example a single panel on a 75/10 takes care of the starter battery while the rest on a bigger MPPT charges the leisure battery directly.
In my 4x4 i have the MPPT connected to the starter battery because i want to give that priority. And of course the alternator is also on the starter. On the leisure battery there is an AC charger. Whenever one of the batteries is being charged the cyrix takes care of the other.
In my installation, I solved the charging (maintenance) of the starter battery from the solar panel in the following way: I used the “LOAD” output on the MPPT 100/20, which I turn on in the range from 13.42 V to 13.6V (user-defined algorithm 2: OFF<13.42V<ON<13.60V<OFF) and inserted a diode between the on-board and starter batteries that can handle a current of 30A. The diode ensures a voltage drop (0.7V) and the direction of the current only from the LiFePo4 battery towards the starter battery. My starter battery is maintained at a voltage of 12.9V, with the current flowing from the LiFePo4 to the lead starter battery reaching a maximum current of around 1.5A. I can remotely turn the LOAD output on, off or configure it in various ways. In addition, I have also inserted a switch that manually interrupts the path “Lifepo4 - diode - Starter battery”. You can also include a 12V 21W car bulb as standard as protection in the circuit, which will serve as protection against high current (the higher the current flowing through the bulb, the more the filament heats up and the more its resistance increases - a very simple and historically proven self-regulation) 
Maybe this idea of mine will help someone or inspire an even better solution.