Any battery experts out there

Hi there

I have a hilux with a dual battery set up, both batteries are normal wet cell (Not deep cycle), the system is controlled by a large isolator switch (The big round dial with 1,2, both and off options) no smart switches or anything else like that.

The accessory leads all run to one battery and I have been told that it makes no difference what battery these leads go to as the isolator switch transfers the current to either battery.

ie battery 1 has the engel cables on it and when I get to camp if I switch the power over to number 2 on the isolator, then the engel is supplied power from battery 2 despite the leads actually being attached to battery1.

Reason for asking is that i want to fit a deep cycle battery and would appreciate the advice as it may prevent me from having to extend all the cables.
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Reply By: Nomadic Navara - Saturday, Jun 27, 2009 at 17:03

Saturday, Jun 27, 2009 at 17:03
"The accessory leads all run to one battery and I have been told that it makes no difference what battery these leads go to as the isolator switch transfers the current to either battery. "

This only applies whilst you have the isolator switch closed.

The whole reason for having an isolator switch is to isolate your load (fridges etc.) from the starting battery whilst your motor is not running. You should be opening the isolator switch when you are camping so you are able to restart your motor in the morning and not have two flat batteries. If you are not working that way then the isolator switch is a waste of flipping time and money (WOFTAM.)

When you install your deep cycle battery there is even more reason for isolating your battery when the motor is not running. Whilst two dissimilar batteries can be charged successfully with an alternator it is not a good idea to discharge them when connected together in parallel.

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AnswerID: 372097

Reply By: RV Powerstream P/L - Saturday, Jun 27, 2009 at 17:13

Saturday, Jun 27, 2009 at 17:13
Peter is spot on with his response but do you want to add an extra battery as a deep cycle or change an existing battery for a deep cycle.
So is it to be two batteries or three.
AnswerID: 372099

Follow Up By: Member - ranger1 - Saturday, Jun 27, 2009 at 21:06

Saturday, Jun 27, 2009 at 21:06

I am wanting to replace on of these batteries with a deep cycle battery as I often stay for a day or two without running the vehicle.

There is also an inverter that I use and it seems to make sense to use all this on a deep cycle battery rather than solely a cranking battery.

I usually isolate the batteries weekly (Alternate between switch 1 and 2 on the alternator) If going for a decent run without the fridge and other stuff will run the switch on "Both" which in my mind charges both batteries at the same time.

Trying to get my head around how a battery can supply power to a fridge if the fridges power leads are not connected to the battery in question.

Does the isolator act as a relay or something sending the power via whatever battery is chosen on the dial.
FollowupID: 639395

Follow Up By: RV Powerstream P/L - Sunday, Jun 28, 2009 at 07:15

Sunday, Jun 28, 2009 at 07:15
The Switch I am aquainted with is the Cole Hershey and it has 1and2 , Both and Off.
That gives you either batteries independently where "both" parallels 1 & 2 batteries so when you are on both you draw from both and it would be better to use like batteries.

If you stay with using 1 or 2 then you are treating them as individual batteries and you could fit a deep cycle.

I removed this Cole hershey from a vehicle and with the new Sterling ProSplit R I would have no need to use a rotary switch.

The ProSplit R takes the alternator power in and distributes to individual channels safely and maintains what is connected to each channel as an independent battery and it also stops backfeed.

The smallest is 12V 120A and 2 Channels but they have 4 outlet ones .

Your existing wiring at the rotary should allow one to be fitted in place of the rotary but it is slightly bigger than the Cole Hershey that I have.

If you are aware of the shortfalls of the rotary on both and only use it as bank 1 and bank 2 then you could just fit a deep cycle for your camping needs.
FollowupID: 639417

Reply By: Member - Phil G (SA) - Saturday, Jun 27, 2009 at 18:41

Saturday, Jun 27, 2009 at 18:41
Your current set-up is the way I prefer to run dual batteries. But I keep the switch closed (ie 1&2) almost all the time - so the batteries are equally sharing the cranking, the recharging and the accessories when camped. Advantage being the batteries share the loads, recharge quickly and last longer. Disadvantage is that if one battery suddenly dies, it pulls the other one down, so best to use identical batteries. The switch is there just in case you stay camped more than one night and wish to preserve the starting battery. The fridge and accessories should still be coming off the non- starting battery.

Only reason to go deep cycle is if you frequently like to camp without driving your vehicle, and need to run the fridge for 2 or more days. If you go this way, you'll need an automatic isolator.
AnswerID: 372113

Follow Up By: Sand Man (SA) - Sunday, Jun 28, 2009 at 12:00

Sunday, Jun 28, 2009 at 12:00

What is the point in sharing the load across two batteries if you run the risk of flattening both, identical batteries or not?

A practical dual battery system MUST keep the two batteries isolated from each other. In this way the starting battery will never be compromised. You are correct that an automatic Isolator is what is required.

This configuration will also enable a starting battery and a deep cycle auxiliary power battery to co-exist and both do the job they were designed for.

For me, it is purely commonsense.


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FollowupID: 639448

Follow Up By: Member - Phil G (SA) - Sunday, Jun 28, 2009 at 14:58

Sunday, Jun 28, 2009 at 14:58
Gday Bill,
We all know there is no perfect system!! And I like to tailor my batteries to my needs.

In my case I do desert trips and weekends away. I rarely go for a day without driving - batteries rarely run down and get recharged to some extent every day. I run one or two engels, and have a winch.

So, with a pair of Exide Extremes (dual purpose battery) I have batteries that can survive the heat under the bonnet and have 160Ah capacity and 1240cca cranking power.
So I can run two fridges overnight and still have 12.5V in the morning, so neither battery is being run down.
I have a heap of winching power.
I have the least resistance with respect to recharging - so recharging is quicker than if I use a wet cell deep cycle battery (which requires an electronic isolator).

As far as reliability goes, I have a simple kill switch between the batteries so they can be mechanically isolated, should I wish to preserve the starting battery, or suspected a problem with one battery. In practice, I never isolate them. Its a KISS system - there is nothing electronic to break down.

Thats the plus side. The down side as I mentioned is if one battery suddenly dies. I minimise this by using identical batteries and buy them in pairs. I usually replace them every 4 years and then use them in my kids vehicles, so I'm always taking fresh batteries. And I monitor voltage to 2 decimal places, so I know whats going on.

I admit I also have a 3rd battery in the back - an AGM that I take on some trips - Its recharged via a Rotronics isolator and I bought it because I'm doing a few trips now where I stay put in the desert.

Nothing new about paralleled batteries - the HDJ100 LandCruiser and later 3L Jackaroo had them as standard.

Its a very common system at our 4wd club.

FollowupID: 639458

Reply By: Maîneÿ . . .- Sunday, Jun 28, 2009 at 14:04

Sunday, Jun 28, 2009 at 14:04
I would use an Automatic battery isolator, not a manual switch, basically because I'm lazy and I want to leave anything to do with the battery charging system to be done automatically.
I don't want to have to blame myself for having a flat battery because I 'forgot' to change the manual switch over.

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AnswerID: 372190

Reply By: Member - Bucky, the "Mexican"- Sunday, Jun 28, 2009 at 16:08

Sunday, Jun 28, 2009 at 16:08
Try ..............he also advertises on this site

Cheers Bucky
AnswerID: 372202

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