Which battery?

AGM have no life span problems resulting from a lack of use , they have less than 1% self discharge rate per month compared to deep cycle at 10/15% , also deep cycle requires a greater degree of charging ,ie 3stage charger to get maximum life span,,, plenty of info in the archives.

Ring the bloke at Federal Batteries in Sydney on his 13..... number in the yellow pages. Very helpful and will suggest a bettery to suit your needs. He has distributors all over Aust.

Batteries not being used doesn't stuff them as long as they are held at charge, this much I do know. Everytime you discharge them shortens their life. The lower the discharge, the less damage. The theory that discharging deep cycle batts is good for them is a myth. They simply can handle it better than a crank battery.

Cheers,

Jim.

Mate,

My suggestion, for what it is worth and with a fair amount of (expensive) experience under my belt, would be to stick with a simple isolator system and a Exide Extreme as your 2nd battery. The battery will be used every time you start the motor, providing a quicker start-up. It will get charged-up each time you drive somewhere and will provide enough capacity to run your fridge, light/s and inverter when you need it. You will be able to get one for not much more than $100- which is about 1/3 the cost of a decent AGM battery. I wouldn't even consider a deep cycle as they are designed for applications such as those go-fors that the oldies use and leccy wheel-chairs etc, where there is an almost constant drain and then it is plugged in over night to fully re-charge. They are not very good at coping with heavy vibration either.

AGMs are great batteries and would do the job, although I don't believe they like being charged in the same way way a starter battery does (via the alternator); they have a lower threshold (I think it is 14.2v whereas as a starter battery is more like 14.4v).

Cheers,

Roachie

HI
If you do not use your vehicle for weeks at a time ie do not start the engine sugest you put it on a small solar panel to keep the the battery fully toped up whil you do not drive it if you are concerend this is the way to keep the battery fresh
Snailbait

After playing around with dual batteries for years, I now stick to two identical starter batteries. My Aux battery has just died after getting a good workout over christmas and after checking the date (which I always write on the side) it has lasted just over 4 years. IMHO to make any battery last, the most important thing to do is to fit a low voltage cut out switch as this will prevent the fridge from trying to draw more power from a battery that is already flat. Which will do niether the fridge or battery any good. Some fridges have an inbuilt cut out but other assesories will still try and draw power. I find the starter battery charges quicker and for the cost it wouldn't really matter if you only got 2 years out of it.
Tony

Is your research flawed..... said nicely and not meant to make you unhappy!

To run an item requiring continuous current draw you can't go past a Deep Cycle battery...
why you ask, because that is the only reason they are made, start batteries are start batteries, DC batteries are made to deliver power continuously over a longer time!

You then need an isolator, one capable of recharging the DC battery as much as possible, read about Solenoids on the various websites, they will recharge, according to various web sites, only to a maximum of 80%, then on the other hand you can buy a Rotronics which charge 100% for the 2 stage system, or only 95% for the parallel system... which is still 15% more than a smart solenoid.

Good Battery $150, Cheap battery $100
Rotronics $280, Cheap Solenoid $150, inc leads, connections etc

What’s it worth to have ample power available when you want it ??

Hi Timber
I have had deep cycle & starting battery over the years, I now run starting batterys
of the same capicity with a solenoid & believe the latter is by far the best
as roachie & tysmc have already stated, just my own experiance,my trailblazer
has a built in cut out ,to stop the battery from totally discharging, this probably extends the life of the batterys.
Friar