Dual battery setup

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Hi Jerry,

Cigar lighter ports are somewhat limited in delivery by their wiring size. Typically 5 Amps.
However, this may be adequate to keep the auxiliary battery charged enough to serve the fridge.
What type of fridge is it? Brand and model.
How many driving hours and how many parked hours will you be doing? This determines how much power the battery will demand from the cig port when the engine is running. I am assuming that the cig port is not energised when the vehicle is stationary.

Answers to these questions will enable me to estimate the power usage.

In the company vehicle, if the battery and fridge running from it , is connected when you switch off the engine, the battery will supply voltage to the circuits you are trying to switch off with the ignition. That will deplete the battery even without the fridge using some stored charge. At a minimum you may need to religiously unplug the ciggy feed each time you stop the engine.
If the vehicle is a campus system which checks the ciggy drain at startup, it may go into error mode. If the vehicle has a smart, read dumb idea type alternator, the aux battery may not get charged fully even on a long run. A few unknowns there.

If you run the fridge for a few hours and start the car it will most likely blow the fuse on the power outlet, as Alan pointed out the access fuse will only be 5 - 15A

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Jerry, the other way of managing this is to transfer the fridge to the company car and power it directly from the cig port without involving a second battery.
It will depend on the wiring and fusing of the cig port but overcomes any Canbus system problems that RMD has pointed out. ( Canbus, not "campus", bloody spellchecker eh RMD? )

Using this method the fridge will only run when the vehicle runs and will warm-up progressively when the vehicle is stationary. But this may provide enough cooling for your needs, particularly if the fridge is set to a lower temperature to begin with and depending also on the quality of the fridge insulation. You could try it out at home to start with. A bit hairy but it may serve.

Guys, thanks for all the inputs, appreciated.
The car is 2019 Colorado & the fridge is compressor ironman 38L
When driving:
Plan is to use the fridge from the cig port while driving.
Charge second battery from another cig port (there are 2)

When stopping.
Starting the car before plugging it in fridge into the cig port??
When stationary run the fridge from the second battery (portable ~40kg but 5 years old?)
If in caravan park charge the second battery with 240 charger with fridge connected.

Hope it will work?
Thanks for all the advise & recommendations.
cheers jerry

Still need some help, please?

Arc pak specifications

An great feature for those struggling to find room for a second battery under your bonnet is the BUILT IN 7 AMP DC-DC 12V Car Charger that lets you charge up and run your ArkPak via your vehicle’s 12V socket.

Is it possible with my box, please? If I get DC-DC charger with 12v cig plug?

Cheers