Well, if you have a mechanical solenoid your not using an ACR.
Those have relays using contact points, and as well are usually rated for Currents well Below what Mechanical Solenoids can with stand.
Combiners can be Electrically Operated or Manually Operated depending on the type.
Usually, they are connected when Running the Alternator, and disconnected when at Anchor.
Similair to the 1,2, both and Off switch.
Only automatic with the ACR relay.
Combiner Switches allow for charging from the Alternator.
Assuming this is True, A DC to DC chargers would be ideal.
As they are programmable for different Battery chemistries.