Cheap Dual Battery Setup

Submitted: Thursday, Jan 23, 2003 at 23:36
ThreadID: 3073 Views:4742 Replies:8 FollowUps:10
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Everybody seems to be asking alot of questions lately about duel battery setups and i see a lot of different setups ranging from basic to advanced and confusing to not so confusing.
I am just letting whoever wants to know about a basic setup which works fine for me.
I am running a 40litre engel fridge on almost freezer settings and it is still going each morning when i get going for the next days drive and if i want to stop for two days i have to back it off to fridge settings.

My front and rear battery in parallel together with the rear being switched through a relay so when the key goes off, the only battery doing the work is the rear. After the relay towards the rear is a fuse for just in case.

My alternator voltage has been increased by 0.4 of a volt to cater for the extra load of both batteries using the same alternator at the same time.

When the rear battery does eventually run flat i just turn the key and away we go again. The alternator charges the rear battery perfectly, even though the front is also getting charged at the same time.

The rear battery is a gel-cell deep cycle.

I use the winch, cb, uhf, cd player with the front battery and havent had a drama yet.

If no-ones gives a hoot ( disregard message ).......
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Reply By: Member - Nigel - Friday, Jan 24, 2003 at 00:16

Friday, Jan 24, 2003 at 00:16
The purists would be appauled - charging a flooded cell and a gelcell in parallel :)

I'm curious as to where you found a relay with contacts rated high enough to sustain continuous battery charging?

The gel should recover quickly, although usually they like lower voltage than a flooded battery.
AnswerID: 11787

Follow Up By: Voxson - Friday, Jan 24, 2003 at 22:44

Friday, Jan 24, 2003 at 22:44
Hi Nigel..
I found an 80 amp relay in an old electric forklift............
FollowupID: 6753

Reply By: Indy - Friday, Jan 24, 2003 at 09:37

Friday, Jan 24, 2003 at 09:37
How did you get the alternator voltage increased by 0.4 of a volt? I must not have been a Toyota one. If it was let me know how you did it.

Comet batteries in Brisbane have a good cheap plan for a dual battery setup. I have installed it and it seems to be working well. I don't think it would work with a gel-cel though.
AnswerID: 11795

Follow Up By: Voxson - Friday, Jan 24, 2003 at 22:44

Friday, Jan 24, 2003 at 22:44
gq patrol
FollowupID: 6754

Reply By: Phil G - Friday, Jan 24, 2003 at 10:56

Friday, Jan 24, 2003 at 10:56
Common setup at the club is to run two identical starting batteries in Parallel (pos to pos), to basically give you a starting battery that is double normal capacity. Need the big thick battery cables of course and both must be well earthed to the motor as well as the chassis.

The fridge is run through a low-voltage cutout set at a conservative setting (about 11.9 volts), so that if the supply voltage at the fridge falls to that amount, then power to the fridge is cut. This usually equates to a resting voltage at the battery of about 12.1-12.2 volts.

Advantages are - very simple, cheap and no components to fail. There is less stress on the batteries so they last longer. (Diesels like this setup). Both batteries are being used all the time. Winching etc is easier on two batteries rather than 1. Don't have to worry about voltage spikes etc. Batteries recharge quicker without potential voltage drop problems through an isolator system.

Downside is: what happens when one battery fails? In reality, this happens less often, so isn't a common problem. Need to replace the batteries as a pair to be sure about reliability.

I personally use a Rotronics isolator (have done for 15 years), but given my time again, would consider this simpler system.

Phil G
AnswerID: 11799

Follow Up By: Member - Nigel - Friday, Jan 24, 2003 at 22:50

Friday, Jan 24, 2003 at 22:50
That simple system certainly has it's advantages and really is one of the best low cost options. And it's certainly the best option for those who winch a lot.

One disadvantage is it doesn't allow the use of high capacity deep cycles to extend fridge run time. But once again it all comes down to individual requirements.
FollowupID: 6756

Follow Up By: Cam A. - Saturday, Jan 25, 2003 at 10:48

Saturday, Jan 25, 2003 at 10:48
Another advantage is that you get proportionaly more discharge/charge cycles from your batteries the less they discharged.

FollowupID: 6770

Follow Up By: Phil G - Saturday, Jan 25, 2003 at 11:10

Saturday, Jan 25, 2003 at 11:10
I haven't been a fan of deep cycle batteries - prefer to use starting batteries because they recharge quicker and they last well provided you limit their discharge with the cutout.

The later TD Jackaroo and TD 100 series run twin batteries in parallel to improve cold weather starting, so can't be to much wrong with this type of setup.

Phil G
FollowupID: 6771

Follow Up By: Member - Nigel - Monday, Jan 27, 2003 at 08:15

Monday, Jan 27, 2003 at 08:15
Phil, deep cycle batteries are like most things. You get what you pay for. I got a 90Ah Federal from Battery World, which is also rated to have 575 CCA, which indicated that it has a low enough internal resistance to recharge quickly (and this have been proven through regular use).

The other very good option is the Powercel AGM deep cycle batteries that will recharge faster than a starter battery. I haven't tried these ones yet, but will do so next time a battery dies (I've got a 4 year old one in the trailer that surely has to die soon). Details on powercel can be found at
FollowupID: 6798

Reply By: Member - Melissa - Friday, Jan 24, 2003 at 12:38

Friday, Jan 24, 2003 at 12:38
Hi Voxson,

I'm one of the people that has been asking a lot of questions lately about DBS, in particular for our GU Patrol. Past 3 4WD's have had manual switching systems or a solenoid set-up. Never have we run the same batteries. Usually a starter and a h/d or d/c.

Because we would sometimes forgot to switch the manual switch over, we now stick with auto systems. Apart from our forgetfulness, we have never had a problem with either system and have had good usage out of our batteries.

With the GU (4.5L petrol), we can only fit an N50 aux. Plan now is to make the N50 our starter and use the existing N70 spot as our aux. We are going to use a Redarc isolating solenoid. Decision has been made after much research and consulting an auto electrician and also based on our previous good experience with a solenoid sytem.

Personally I've come to the conclusion that the whole DBS thing has become overly complicated. While some of these "complications" may be warranted in certain cases, I think a lot of it is just good marketing.

But, that's just my opinion...

:o) Melissa
AnswerID: 11807

Reply By: Cruiser - Friday, Jan 24, 2003 at 13:08

Friday, Jan 24, 2003 at 13:08
I have recently fitted an ARB dual battery system to my 100 Series cruiser. All up cost including the Battery Separator, Battery Tray, All the required cables cut to required length and ready to fit and a Hybrid Battery (cross between DC and Cranking Battery) was $510. Took just over an hour to fit. Basically my 2 year old son could have fitted it, it was THAT EASY. I too looked at the various forums trying to figure out the best / most economical way to go about it, but felt for just over $500 all up was a good deal and it works extremley well.

I priced up the parts individually, ie, Battery Separator (a Redarc and a GSL one) , getting the cables made, Battery tray etc, and there was only $50 in it. It was easier and quicker to buy an already tested and proven kit from ARB.



AnswerID: 11808

Reply By: joc45 - Friday, Jan 24, 2003 at 15:35

Friday, Jan 24, 2003 at 15:35
I have a GU Patrol, and use a simple H/D solenoid relay to parallel the batteries. To operate the relay, I have taken the Aux output from the alternator. This is usually from a second set of diodes in the alternator, and only gives output when the alternator is charging; ie, just turning the key on will not operate the relay, only when the engine is running. This way, you are not connecting a flat aux battery across your main battery when starting the vehicle. Cheap and easy and reliable.
My last ED5 aux battery lasted over 2 years with this arrangement, and was only eventually killed by external idiot causes.
The Aux output from the alternator is pretty easy to locate - it's one of the smaller wires coming from the alternator, and is used to operate the alternator warning light. A quick check with the voltmeter when the engine is off, then when running will prove it out. The other small wire (on a Nissan) is usually a voltage regulator sense lead which comes from the battery.
Worth getting also is a cheap voltmeter to monitor the battery. Jaycar sell a nice LCD unit which doubles as a int/ext temperature guage, for about $40.

On my earlier GQ, I found that a diode splitter caused radio interference due to commutation of the diodes. (tho it can be fixed with capacitors)
AnswerID: 11811

Follow Up By: Bonz - Friday, Jan 24, 2003 at 21:39

Friday, Jan 24, 2003 at 21:39
Joc I looked on the jaycar site and coudnt find the temp/voltmeter unit you mentioned. do you have a part number r similar so I can go there next week (in Melb)?
FollowupID: 6747

Follow Up By: Oziexplorer - Saturday, Jan 25, 2003 at 00:09

Saturday, Jan 25, 2003 at 00:09
Part No. XC0116
I have one of these fitted in the back of my vehicle. I use the Outside tempreture probe in my fridge to make sure it stays between 4C and 6C and the volt meter lets me keep an eye on my auxilliary power battery. What surprised me, the voltmeter is accurate against my standard volt meter. That pleased me no end.
FollowupID: 6765

Follow Up By: Joc45 - Saturday, Jan 25, 2003 at 14:52

Saturday, Jan 25, 2003 at 14:52
Thanx for that, Ozi,
Has inside/outside temp, a clock/calendar, a low voltage warning light, and a critical low voltage beeper. Also an ice warning - that may need to be disabled if you are using the external sensor in your fridge.
Mounts easily (double-sided tape), and looks fine. It has a blue backlit display, which stays on all the time, but this wouldn't draw much. Just need to remember that it does use a small bit of power.
Jaycar also flog a cheaper unit, but it doesn't have a temp guage, only a stopwatch. XC-0118, $34.95. Get the more expensive one.
FollowupID: 6776

Reply By: Eric - Friday, Jan 24, 2003 at 23:05

Friday, Jan 24, 2003 at 23:05
Congratulations on not being sucked in by sales people. if you want to perfect your your set up you can reduce you alternator back to the correct voltage to increase you battery life, and then move the connection to your soleniod from the starting battery to the alternator output terminal this will give you the extra .4 volt that is normaly droped in the wiring loom this also limits the current during starting so you only need a 30 amp relay. Eric,
AnswerID: 11833

Follow Up By: Voxson - Friday, Jan 24, 2003 at 23:19

Friday, Jan 24, 2003 at 23:19
thanks for the little hints eric...
FollowupID: 6760

Reply By: freddy - Saturday, Jan 25, 2003 at 15:39

Saturday, Jan 25, 2003 at 15:39
thank you joc45, you are a godsend. i had been trying to find a suitable voltmeter for my dashboard for ages and was about to pay $200 to get one from japan. a quick trip to jaycar this morning and i am now very happy...
AnswerID: 11857

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