ARB dual batteries...setup???

I got the Piranha system from Piranha in Bayswater, happy with it, comes with everything you need. ARB system should be the same.

Run GOOD wire down the back, its worth doing once and doing right.

Is it only going to run the Engel?

I cannot answer all of your questions at the moment, because there is some calculation necessary. You should post the equipment you'll be running off of the aux. battery, and the amps they require. Also, how long you want to run things whith the engine off (camping).

Regarding the fuses, keep this in mind: Any wire that is connected to the battery's + terminal, and runs out to an appliance or piece of equipment, is vulnerable to "shorting" out. This happens when the wire's insulation is compromised, or the connector comes loose and the bare wire (conductor) comes in contact with any metal from the vehicle. The electricty will now find a "short"er path and try to return to the battery via the frame or body of the car. This will cause the wire to become overloaded with current and it can get hot and start a fire. So, to protect any wires you have traveling along your vehicle, you should install a fuse as close as possible to where that wire is getting it's power from.

To organize your wires and connections, and fuses, you can run one big wire from the aux. battery to a fuse block (or "distribution block") and the block will have many terminal connectors for you to connect accessory wires to. This way you do not have to connect a whole bunch of wires directly to your battery post. In this case, you would want a fuse on the big wire that feeds the distribution block, as close to the connection to the battery as possible.

Andrew,
I've had the ARB setup in my 3.0 GU for 2yrs now. I bought the battery tray, smart separator & wiring looms, and installed it myself (ARB sell it as a kit). Pleased I did this as the installation is a breeze, with well documented instructions. I bought an n70ex (exide extreme) battery. I ran a cable (fat wire, used in industrial switchboards with double insulation) through the firewall on the passenger side, along the "cable tray" under the kick plates on the doors, to three separate power points located on the panel adjacent to the smaller rear barn door.

This has served me well, ensuring a ready supply of cold beers (45lt waeco), sound for the kids, powers an inverter for lighting, and recharges various AA sized batteries.So much to see, too little time ...
Andrew

I had ARB install their standard dual battery system in my 3.0TD GU as soon as I got the vehicle last November. Had power points installed in the dash and two in the rear. 40l Engel has run continuously since then.

Don't know the technical stuff 'bout 'lectricity, so wasn't game to do it myself. No problems with their system or the way they installed it. Hasn't let me down yet.

Andy
Just a note about batteries
Don't forget that you cannot run a deep cycle battery below about half of its stated AH rating without risking some decrease in longevity. A cranking battery can only be drawn down to about 3/4 of its capacity but I have been told (not by a "pro" however) that the gel-cell type can be run nearly flat. That is why a 45AH gell cell will perform as well as about an 85 AH wet cell but is much smaller in size. But I may be proven wrong about this.
Something for you to check out.
Cheers
Oskar

Andrew
I checked some details regarding gel-cells vs wet-plate batteries with a friend of mine who designs and builds circuits for power generating companies around Australia. (He's the specialist they get in when the experts can't solve the problem)
He threw some extra light on the subject.
You may already be aware of this information (or some of it) but here is what I have found out of late
1) Gell-cells should not be charged beyong about 14.1 volts or damage can occur.
2) Wet-plate batteries need around 15.1 - 15.5 V to be fully charged and to ensure their longevity (Most manufacturer alternators peak at about 14.1 V I believe)
3) In hot weather (summer/tropics) wet plate batteries charging over about 14.4V will probably boil the electrolyte away. This doesn't conflict with point #2 neccessarily. Some shielding of the battery from engine bay heat is desireable.
4) If using a wet plate main and a gell aux you need to make sure the charging system is compatible with both batteries due the different needs of each.
5) Existing alternators can be modified with an external regulator and a charging diode to "up" the output voltage to 15.1 - 15.5V.
6) Wet-plates which do not get fully charged will always fail sooner than those which are.
7) Wet plate batteries should be "brought to the boil", for a period of time, overnight perhaps, (fizzing/bubbling) to allow full-charge to be achieved. (It removes the sulphation or something like that) That doesn't mean that you boil it on the stove or anything like that, but that the charging system must have enough kick to do the job.
I hope this adds something useful to your knowledge of the topic
Cheers
Oskar