Motolite Deep Cyle batteries

Thanks Ozi - I pushed the wrong button - my reply to you shows as a reply to my question ... it has been that sort of day!

Nick

If you are going to use a three way fridge then a substantially smaller battery would be more than adequate.
A battery like the Apollo 862 75aH - probably, around $115.00
The life span of a normal deep cycle battery is normally twelve to fifteen months, so no advantage to have a larger battery than is necessary, or spend more money than is necessary.

Are you aware that three way fridges do not work well while travelling if the roads/vehicle is rough. If you are only travelling short distances, or you are on smooth roads, this is not an issue, However, if you are travelling through bush tracks more than one day, this does become an issue.

With the saving you will make on the battery, when you go away and camp for the three week period, you could invest in a small Solarex 20w solar panel for $268.90 from here:
http://www.biasboating.com.au/solarpanels.html
If you went away camping only in summer, then a 10w panel at $168.90 would make the grade. You would need to change the orientation of the panel three times a day. With your fridge running on gas and the use of a couple of fluoro lights and UHF radio should supply you with sufficient power.
The other alternative is not to use a extra battery at all if you only want to run the UHF and a couple of fluoro lights. You could use an Exide orbital from here:
http://www.exide.com.au/pages/batteryrange.html
and put the money from buying the extra battery and Arrid system towards the cost of the solar panel. The only other addition I would put on the system, would be a low battery voltage cut-out so that you did not accidently run the battery flat so you could not start your vehicle. This would be unlikely, but with kids, anything is possible. The low voltage battery cut-outs can be purchased in kit form cheaply from Dick Smith Electronics.
I have no idea of the price of the Exide Orbital batteries and have no personal experience with them. The surveyors whose DGPS gear I borrow use them in their vehicles and for running their electronics while stationary and are reporting good service from them. With this type of battery using it for two purposes, I would change it every two years.

Exide Orbitals are around $280-$300 - still a bit pricey for a 55 Ah battery, unless you definately have a reason for needing a sealed battery.

Nigel I had no idea they Exide Orbital batteries are that expensive. Will get some local pricing tomorrow as a matter of interest.

Colin on normal wet cell deep cycle batteries I think all companies only offer six months.
If you are talking about www.cyb.com.au Yuasa, then my statement is correct. If you are talking about Global Yuasa, then my statement is also correct.
On normal automotive and truck batteries two years is the norm. The life of a wet cell deep cycle battery is normally maximum 18 months (being generous)