Some versions of the Multiplus have a trickle charger built in. This only works if the starter and engine batteries are the same voltage (both 12V or both 24V). See the linked FAQ. Care is needed if the domestic bank is lithium because in some cases this could be problematic, the FAQ covers these.
I used to use the Multiplus trickle charger when I had lead acid domestic batteries but now I have swapped to lithium I have changed to an Ablemail trickle charger. As this can cater for lithium and is properly voltage controlled. Many of the trickle chargers like Votronic and Van Blitz are just a current limiter/diode circuit like the Multiplus circuit so have the same limitations.