Car fridges and batteries?

[Houses4Rent]

Am I right in saying that running a 12V fridge in a vehicle is only possible in statioary vehicles when there is a secondary battery installed to run it? Otherwise it would drain the primary battery fairly quickly? I am looking for weekend outings off grid (camping) and need to keep things cool, but do want to bother with complicated battery setups in a normal car (not kombio, not 4x4).

Urgent responses appreciated as I am looking at some fridge specials.

[AndyD]

I'd certainly advise using a second battery for a fridge unless you invest in an intelligent monitor that will limit the depth of cycle on the main battery. Also using a standard car battery is going to destroy it, theyre only designed to be cycled to about 20% of their full charge, you need a deep cycle battery.

[Justloadit]

Car batteries are not really designed for cyclic use as driving a fridge. They are designed for high current for a short time. Draining to many times will render the battery inoperative.

Secondly using your primary battery in an off road situation will land you up in the dwang if it is flat. How do you start up your engine then?
I suggest that you have a second battery, deep cycle for the fridge, however depending on the fridge size and inverter, it may only run for a few hours. Lets take one of the absorption fridges, which has 3 types of ways of usage, 12V, 220V and gas. The heating element requires 100 watts per hour, so using the 12V battery means that you will get about 7 to 8 hours use out of a 100Amp deep cycle battery. Not much for a weekend.

I would rather use gas in the absorption fridge, as a bottle of 9Kg gas will last about 90 hours. I would also get a small 900W generator as part of my kit, just in case my battery died in my vehicle. At least I could charge it with the small generator.

[Houses4Rent]

Thanks Justloadit, as I thought.