Auxillary battery sizes ?

Daniel,

Depends on the current drawn by your gear, and how you charge your battery. You really need to have a way of measuring this. A cheap multimeter will do the job, but it MUST have a 10 amp range and you must be careful using it. (Above all don't connect directly across the battery when it is set up to measure amps. For safety (of the meter) always leave it set to the 20Volt range unless you need it for a particular current measurement then change the setting back immediately after). Jaycar, Dick Smith etc will have something suitable.

Check out our electricity blog, Electricity for Camping for some useful numbers .

Basicly, if you are running a fridge, I'd aim for a battery of at least 100 amphour capacity, more if you want more than 2 days out of it without charging.

HTH

John

Dan if you are having problems with 2 different batteries then there is a possibility the wiring to your fridge is undersized or the plugs are causing voltage drop.
I'd confirm the batteries state of charge (volts & hydrometer) to see if they are in fact flat when the fridge stops. If not then test the volts at the battery & at the fridge while it's running to see if there is a large voltage drop.
How long do you need it to run as this ultimately will determain how large you'll need to go?
Cheers Craig............

Hi Daniel
Your fridge will draw around 4amps while actually running. the actual run time will be affected by:- ambient temp ,thermostat setting[ the colder you set it the longer it will run] & how warm & how much warm stuff you put into it.
You should be using a deep cycle battery for this sort of application , they are designed for this type of duty & a standard cranking battery is not.
Deep cycle batteries are rated in amphours of capacity & for long life should not be regular discharged below 50% of their capacity
A 100amp hr battery should only have 50 amphrs taken from it before recharging.
As I said if your fridge draws 4apms , it will use 4amphrs per hour of actual running time.A 100 amp hr battery will run it for 25hrs actual running time.
HOW LONG IT ACTUALLY RUNS FOR DEPENDS ON HOW YOU ARE USING IT
If being used as a fridge,not a freezer, this actual run time could be 8<12+hrs per day

Hi Daniel

what size wire have you used from fridge to battery (actual diameter of wire... not including insulation)?
how long is this wire?
what type of connections do you have?
what is the rc stated on battery?

I have a N70 starter battery and get 10 hrs runtime without starting car (about 42amphrs used) but I know this is not good for the battery and try to avoid it.

regards Kc

hello to all
My appologies for the late follow up ( shift work can do that to you). Thanks to everyone for the advice. Sounds like the first thing to do is check the charge of and to the battery then the draw of the fridge. thanks again
Dan