Split Charge Battery, fridge relay
These 12V voltage-sensing relays come in 22 amp and 30 amp versions.
They switch power to a campervan, caravan or motorhome's battery-charging and fridge circuits when vehicle alternator is charging. It protects the vehicle battery from draining down when the engine is off.
These relays use voltage-sensitive switching, so they require no trigger.
They can also be used to automatically disconnect the fridge from the leisure battery when the voltages drops to below 12volts, to protect that battery from being drained too low.