Thread: Dual Batteries

Originally Posted by JamesH

My system is similar to KhunMoo's but it has a simple two way switch A, A+B. Running the car on B only is not a problem (both A & B are normal cranking batteries). The thing that leaves me uneasy about it is that EVERYTHING is connected to the main cranking battery even the 12v plug in the back. I'd like to at least have the rear plug attached to battery B. When I had the car at an auto-electrician getting a new clamp for the batteries and a new switch that wore out I asked them to re-wire the back plug to battery B but he talked me out of it. He said the system I have is nice and simple and apart from the switch wearing out is bullet-proof. If you are disciplined about isolating the B battery when pulling up to camp, you always know where you stand with it. You have one fully charged battery sitting there ready to start your car in the morning.

Anyway for 99% of the time the switch is set to A+B so both batteries crank the car, it's only when I have the fridge in the back I ever isolate.

I fear flat batteries in the bush more than I fear crocs and king browns...

Just my 2 cents worth James, I have the same system and only have either bat A or bat B selected at any one time. The beauty of the system is its simplicity and having A+B connected would in my opinion be asking for trouble. I would only use it like this if jump starting a vehicle with flat battery. BTW all accessories run off the battery that is selected which gives you a good battery always for starting.

Yep I agree with you Bushie. My work Nissan has been flogging around the Kimberley with me for 5 years now and it has one of those ARB smart relay set ups (not very smart actually). We have been caught with two flat batteries at least 5 times because you never know what is going on. As soon as one cell in one battery drops you end up with two flat batteries next morning and not the slightest warning that it is going to happen.

Our new truck will have a Cole Hersmann switch and a voltmeter.

KhunMoo