I have earthed mine to the chassis but my crank battery is earthed to the motor iam going to put a 100amp fuse at both batteries Cheers Richard

 

In my case i earthed the aux battery to a captive nut in the chassis rail below the battery using a lead i has made up at a local battery world. The body and chassis should both be grounded equally but going direct to the chassis ensures the best ground by avoiding resistance that might exist between the body and the chassis connections under load.

I used a jumbo fuse close to the aux battery because i ran a heavy cable to the rear. If that cable ever gets damaged and shorts i know the fuse will blow as opposed to discharging the entire battery into the chassis or body and causing a fire.

Grogey

 

What amp fuse are you using?

In my case i earthed the aux battery to a captive nut in the chassis rail below the battery using a lead i has made up at a local battery world. The body and chassis should both be grounded equally but going direct to the chassis ensures the best ground by avoiding resistance that might exist between the body and the chassis connections under load.

I used a jumbo fuse close to the aux battery because i ran a heavy cable to the rear. If that cable ever gets damaged and shorts i know the fuse will blow as opposed to discharging the entire battery into the chassis or body and causing a fire.

Grogey

 

Best bet is to connect the main earth for the second battery to block or alternator.

This should ensure the best possible earth connection for the charge circuit.

Then depending on how you wire up your accessories to run off the second battery, you can also run another earth to the body.

The GUs especially the early ones were notorious for having a bad earth to the chassis.

Yes you should have it fused.

 

I have batt cable from neg.post to neg.post of both batts. Plus aux, batt earthed too body/chassis and motor, Both batts have an inline fuse close to the batts. Earth can be the biggest enemy in a dual set-up. Might be over-kill but never have drama's and know its safe.

 

G'Day... Many of the above replies are right on the money.
My setup is an attempt at being trouble free and ensuring no voltage drop due to resistance with poor chassis /body earthing:-
I run auxillary battery negative terminal (earth) to the engine, and to the body. Then run an earth to the main battery neg terminal.
Then very importantly, put in a heavy lead underneath the vehicle at about the prop shaft behind transfer case. there is a spot that you can electricly connect the chassis to the body to ensure the entire earth through the vehicle is good.
This is also in the GU Y61 Reference document available on here somewhere.
Fusing the positive terminal is pretty easy and extremely important. Things do go wrong and 4WDs do bounce around. A fuses purpose is to protect devices so why not? The main thing to be wary of is a dead short, so a relatively big amp fuse is what you want.
I went to battery world and they sell a pos terminal fully fused up with 2 low current fusses (30 amp I think) and 1 high current fuse (over 100 amp I think). Its also complete with a top cover for insulation. If a cable accidently chafes through somewhere, or some other sort of problem, the fuse will let you know.
Good luck!

 

Thanks everyone for their replies, I have bow changed the set up that came in the kit and just added a few different things, much happier with it now, thanks again guys

 

What size fuse would be better from main to aux via isolator ie 250 or 300 amp ive got 330amp cable? Thanks Richard

You ill be replacing them every time you try to start the engine... if you get it started.

The starter will draw a lot more than 200A and if the fuses hold, they will certainly drop the available current to the starter.


I earthed my 2nd battery to the body and the engine block just like the original battery.
This takes the load off the earth strap which are known to cause trouble in time on all cars where they are fitted.
With both positives going to the starter, I can start the engine with either battery disconnected. When both connected, I get plenty of current to the starter and both batteries get hit a lot less hard than one on their own when cranking the engine over.

 

Does anyone have pics of these marvellous set-ups? I plan on installing a DC-DC (Redarc BCDC1220) myself to save on having to bend over for ARB installation charges, just need an idea of what it looks like under the bonnet instead of just a wiring diagram.
Cheers.

 

looking at putting dual batterys in my gu patrol ute simply to run the fridge off of the second battery can anybody tell me what the best dual battery kit for money would be on the market and why. i want something thats going to be reliable maintanence free and worth the money i pay for it. cheers guys