Deep cycle batteries

First of all, a question: have you considered that the charger may be faulty? (causing the white powder "sulphating" you describe) Try using the charger once or twice a month for 6-12 hours just to top up the battery. If there is no load connected to it all you need to do is compensate for the self-discharge that the battery. Sounds like you are frying your battery somehow through lack of use and overcharging.

As far as replacement batteries go, three options I can suggest are:

Odysseyhttp://www.odysseybatteries.com.au/odyssey/default.htm
Optimahttp://www.optimabatteries.com/
Delkorhttp://www.delkor.com/product/product_list.asp

I have personally used the Odyssey in other areas and found their characteristics to be well suited to deep cycle work(400-500 cycles to 100%) and capable of rapid recharge with no ill effects (lees than one hour from 0 to 100% charge), with a 5-10 year life, but they are a bit pricey.

Perhaps some of the other forum members could share their experiences with the other two types of batteries

Chris, why don't you try W.A. Solar Supplies (not to be confused with
W.A Solar Sales) in Osborne Park for a good price on deep cycle batteries. In past forums I have mentioned the Magnum batteries I have been using & the reliabilty & long life I have been getting out of them when they are recharged properly much to some controvertial comments from other people on this forum.
So all I can say is go and see for yourself these batteries. The address is Unit 5/83 Hector St. Osborne Park telephone (08) 9244 2668. Have Wheels Will Travel

Chris, I have my solar panels connected to me deep cycle battery all the time & this ensures the battery is fully charged even when not in use. Make sure you get a good quality solar panel charge regular (with pulse charge ability) in the setup. The "Arrid' regulator sold by the 12 Volt shop in Welshpool is a good one for around $75. Cheers.Have Wheels Will Travel

The sulphation of your battery is caused by natural discharge while in storage. You need to get one of the "charge and maintain" type chargers, this will ensure your battery is always at full charge. The other next big item that affects the battery's ability to store charge is temperature. Batteries should be stored in a cool dry place as your battery will self discharge twice as fast if stored at 35 deg c than if it sat at 25 deg c. I found this all out the hard way after killing two big deep cycle batteries over 18 months. Unfortunately they did'nt cover warranty the second time around. The manager cited incorrect storage practices as the cause of sulphation but gave me a replacement at cost and a copy of a web site document on battery storage.

Chris,
Batteries have to be fully charged when not in use or they sulphate, causing the white powder, maybe the charger could be too small to get enought power into the batteries, on the back of the box it gives a clue as to what size battery they will charge, the big one is 'sposed to be rated @ 10 amp. you can get a trickle charge unit to fit onto your charger from the same manufacturer as your charger, leave it on permantly while Disconected from vehicle and I'm sure you will see a difference.
Charge the battery only while disconected from the vehicle.

I use two 80 amp/hr Delcor batteries ($135 ea) wired in parellel, with assistance from a 80 solar panel while I am camped.... my fridge/freezer runs without hassles at only 1 degree in fridge & -14 in freezer..... it is not an Engel.