Batteries in parallel. What'sthe go......?

My understanding with this configuration is that if a cell shorts then that battery will drag the other down to a condition where we may be able to listen to the radio but we wont be going very far till the vehicle is either crash started or another charged battery is brought into play. I think I'd rather avoid that possibility especially if travelling solo or just to avoid embarrasment.

yep...agree, good battery will try and dump its load to crook battery.

Hi Ray,

Yep, you've pointed out the downsides of that setup. Especially the bit about travelling alone outback. The other downside is that you want a low voltage cutout set a bit higher than the ready made ones - but thats OK if you're handy with electronics and can adjust up a Jaycar kit. And naturally the batteries need to be identical in every respect.

There's some upsides. Simplicity, reliability and cost. You've potentially doubled your CCA. And running the fridge for one or two nights won't draw the battery down as far. So they tend to last longer. They should also charge up quicker than an isolated system.

The 100series TD LandCruisers and later TD Jackaroos come standard with this setup to aid in cold weather starting.

Many friends at our club run their batteries this way.

Cheers
Phil

I have seen 3 vehicles set up this way and every one of them has had problems as you cant isolate the batterys to check them and then isolate a crook battery and the crook one theives the charge off the good one so you think everythings good until it doesnt go

G'day Willie and others,
Just going thru this trouble myself on camper trailer. Have 2 Exide Orbital spiral gel cell batteries....one is 33months old the other is about 8 months old.
I had to go away for about 10 days recently, leaving the trailer in the garage. Whereas I usually leave the 3 stage charger on 24/7 to keep the batteries fully topped up, I have been having some reservations about the state of the electrics in the camper, so I turned the charger off before I went. I made sure that everything was isolated, so there was NO drain on the batteries what so ever. Checked the batteries when i returned and 7.98 volts!!!!!!!!!!!!!
Just an hour or 2 ago, i pulled them both out of their compartment and checked them independantly (ie: once I'd separated them). the newer one showed 12.38v and the older one 7.98v.
So now i know why I'nve been having troubles!!!!
I've now decided to put the "good" one in the back of the Patrol to make a 3rd battery in it (I have 2 x Exide Extremes under the bonnet) and I will now get a 120 a/h Calcium or AGM battery for the camper. That way I will have about the same (or more) a/h than the 2 Orbitals had anyway, and they will be in one package so I won't have the problem of a good battery "masking" a weak/dead battery.
I'm still happy with my dual battery set-up on the Patrol which has a manually operated isolator. I will simply connect the Orbital in the back of the Patrol to the 2nd battery.
Cheers,
Roachie

David, yes correct but it's important to present Willem with the facts so he can make an informed decision on what suits HIS circumstances armed with the facts. It's no getting caught short in the bush and then saying "nobody told me that could happen"

Personally I would never operate without an isolator because I make extensive use of a HF radio not only for voice but data that is controlled by a computer and transmits periodically unattended drawing over 20 amps....just too easy to flatten batteries if not very careful. My point here being we have different circumstances and expectations.

By the way, with the redarc it is simply a matter of grounding one little wire to parallel the batts, can be done from inside the cab with a switch. With some simple electronics both batts can be left paralled until the main drops to a preset level and then isolate automatically.

No matter what the system there are positives and negatives (pun intended) if we are aware of the negatives we are forearmed

Mad Dog,

You are correct. Go for what suits the owner. Yeh I know about the bridging on the redac etc but the installer forgot to tell me that and I had to wait ages for a jump start when all the time I had a good battery.

I just assumed that they would both come in to play for sarting.

Jeff, can you setup an independent battery and attach a solenoid in the usual manner, then add an aux battery to the solenoid, forming a sort of ‘fully independent’ dual battery system that will never get charged or have any electronic leaks, because they are both removed from a vehicle and not grounded independently.

Obviously both batteries initially should be fully charged 24 hours previously and the ‘isolator’ has to be ‘activated’ by the current from the starter battery as is the usual practice in the conventional dual battery system.

Test the voltage at both batteries independently, and also each side of the solenoid, with the solenoid in both the open and also the closed situation, and then do the same with a Piranha (or similar) electronic system for a comparison!

Now you have another excuse for some tinkering....

Except I don't have a Piranha... I had an electronic one but it pooped itself, hence going back to relay tecnology. So far so good with this latest experiment, but I'll wait for my camping trip in two weeks down south the see if it actually works the way I think it will. Then I'll post what I did and the resutls. If it does'nt work, I slink off into the distance and won't say anything! LOL

Hi Willem, I have my batteries in parallel and have one of those $10 manual isolators with the green knob on the auxiliary battery. i have a Liemack fridge so you need both batteries to get you through the night, they suck power like a jet ... The point is you can just pull the bonnet and undo the knob to isolate the auxiliary battery with a normal fridge,it takes a few secs only and you always have heaps of cranking power with both batteries connected. It's better for the batteries, they are allways both fully charged. Michael

Alloy

My Rotronics MH10 was bought mid 2002 and fitted to the G60. Then it found a home in the GQ. So it worked for about three years.

I am still on the road and will send the unit back to Rotronics so that they may have a look at it. I only discovered that the Isolator wasnt working as my new battery started failing and output dropped below 10 volt. The battery came good when I hooked it up in parallel to the other one.

Will post result of finding sometime in the future.