GU CRD battery setup

I had a 2010 GU Patrol and used the SBI12 without any issues, it was paired up to an AGM100Ah which fed the Waeco for 4 days whilst stranded at Mungerannie

Cheers

Colin

Lachy,

I am not aware of the output of the Patrol Alternator but it may be that it is not enough to efficiently charge your auxiliary battery.

The Redarc SBI12 is a dual battery isolator which keeps the primary (starting) battery electrically separated from the auxiliary battery. Should there be a heavy draw from a device connected to the auxiliary causing it to go flat, the isolator will stop the same thing happening to the starting battery.
This is the whole purpose of an isolator.
When the vehicle is first started, priority is first given the charging the starting battery, then after it has reached a minimum voltage level, the isolator will connect the auxiliary battery and charge that. How good a charge it gets depends on three things.
1. The output capacity of the alternator
2. The thickness of the cable to the auxiliary
3. The distance from the primary battery to the auxiliary battery.

A dc-dc charger has the ability to boost the voltage coming from the alternator so that the remotely mounted auxiliary gets an optimum level of voltage. A dc-dc charger usually has a built-in isolator so it does the job of both devices.
The amount of current available to put into the charging process will also depend on the above 3 "things" but is less important than the voltage level as the level of current will basically affect the time it takes to fully charge the auxiliary.

A simple test you can perform is to connect a multimeter across the auxiliary battery and measure the voltage across the terminals. After the initial running of the engine of a minute or so, the circuit to the remote battery should be active and you need a voltage level of 14.2v plus, to keep the remote battery charged when in motion.

On my vehicle, I get sufficient output from the alternator to charge the auxiliary battery mounted in the tub, but use a dc-dc charger in my camper trailer to get a high quality charging process to the two batteries in the camper.

A dc-dc charger should be mounted as close as possible to the remote battery location.

I have a 2010 CRD. The alternator is perfectly fine, particularly as you have the same type of battery as your starter. DC-DC chargers have their place but your application doesn't require one IMHO. Many on the Patrol forum have the same setup as you (or similar with a different branded isolator).

Adrian

I have a 2007 crd with dual wet cell batteries under the bonnet connected in parallel,no isolater,on occaision i add a third battery behind the cargo barrier (again wired in parrallel no isolator) seems to work well

Seems that the advice from your ARB store is not consistant across the ARB network.
I have an ARB aux battery tray in my 2011 GU wagon - fitted it myself, and there was no mention regarding the unsuitability of the Redarc SB112 isolator, in the fitting instruction.
My aux battery is a Century Marine Pro 720 N70ZM, and it is isolated with a SB112.
It is usually returned to 14.2V in a short time of running, provided the aux system hasn't been used. Recovery time varies depending on camping use.
I have 2 voltmeters - one on each battery.

Recently I did have a problem - a trap for the unwary. I had a Total Knee Replacement and the Patrol sat in my garage for 5 weeks without being started. When I tried to start it the starting battery was flat at 11.6V. The aux battery was 12.6V.

Investigation showed that a number of low draw items on the main circuit had depleted the voltage on the main battery. ECU memory, radio memory, clock, imobiliser and alarm, and another one that never occured to me - the Hayman Reece electric brake controller!

I will put a switch on the 12V supply between the battery and brake controller, so in future I can isolate it. Or alternately I could connect the controller to the AUX battery.