Victron - Skylla-TG 24/100(1+1) 230V [SDTG2401001] Diode Isolators The Cyrix Battery Combiner is

The Cyrix Battery Combiner is a microprocessor controlled heavy duty relay that automatically connects batteries in parallel when one of them has reached a pre-set voltage (indicating that the battery is being charged)

so the Multi or Quattro can reduce or stop charging when the battery temperature drops too low

Similarly to Argodiode battery isolators

which is for Victron Lithium Battery Smart batteries)

Victron - Skylla-TG 24/100(1+1) 230V [SDTG2401001] Diode Isolators The Cyrix Battery Combiner isOne full rated output and one 4 Amp output. Charge voltage can be precisely adjusted to suit any battery system. The input for the charger is 230V at 50 60HZ. Charge voltage can be measured directly on the battery terminals in order to compensate for voltage loss due to cable resistance. An external sensor allows measuring battery temperature and compensating charge voltage accordingly.