Deep cycle Battery question

I have a dual battery in my 100 series with a Red Arc that charges the Aux Battery. The other day I noticed that the Deep cycle battery has started to leak or overflow ( dont know which yet) but when I put the multi meter on it it read 4.9V. I am no electric wiz so I am assuming that it is dead. I have had the 100 series for 2 years & the set up was already in so I don't know how old the battery was. My question is that I will only use the Aux battery to run a fridge when on trips. So is it fine to put in a new AGM battery that will not be getting any use until my next trip in september.Does the contant charging from the red arc when the main battery is charged do any harm if I am not using the Aux battery at all?
Should I just put in the Aux battery when needed and just store it & keep an eye on it and charge it with my Ctek charger to keep the volts up every now & then?
Any feed back appreciated.
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Reply By: Notso - Sunday, Jan 31, 2010 at 20:36

Sunday, Jan 31, 2010 at 20:36
At that voltage you'd have to think it was had it. It's possible that there is something amiss with the Redarc.

What voltage is at the second battery terminals when the engine is running.
AnswerID: 401965

Follow Up By: Notso - Sunday, Jan 31, 2010 at 20:37

Sunday, Jan 31, 2010 at 20:37
Have you checked the electrolyte levels in the battery?
FollowupID: 671386

Follow Up By: mono2 - Sunday, Jan 31, 2010 at 20:45

Sunday, Jan 31, 2010 at 20:45
With the engine running it had a max of 8.1V.
Have not checked the electrolyte levels as I dont have the tester. But I did notice that there was 3 cells that were very low and topped them up. Didnt seem to make a difference.
FollowupID: 671390

Reply By:- Sunday, Jan 31, 2010 at 21:41

Sunday, Jan 31, 2010 at 21:41
mono2, to answer your questions:

If you don't need the second battery for the next nine months, don't put it inside the vehicle as yet.

It'll have a much easier life if you put it in a cool spot and do some maintenance charging every three months or so (in case it's going to be a new deep cycle AGM VRLA battery). Flooded batteries self discharge faster and need more regular maintenance charging to prevent them from getting sulfated.

Since you don't know yet, why the one battery has died, it would be good if you could put any battery in its spot and have it test charged by the redarc.
Make sure the boost voltage doesn't exceed 14.4V/14.7V (for flooded/AGM). The final float voltage should be around 13.7V for both.
Note that for every 10 degrees above 25, these voltages need to be reduced by approximately 0.25V.
That's why, for in situ charging in hot environments, temperature compensation becomes almost mandatory.
Does your redarc have an external temperature sensor which can be attached to the battery?

Also make sure the redarc reduces the boost voltage to the float voltage level with the fridge connected.
Some multistage chargers get confused because they can't tell battery charge currents from load currents.
The result would be dry out of your deep cycle battery because it'll be sitting on 14.7V for prolonged periods of time.
Top of the range chargers prevent this from happening by applying adjustable time limits to the boost stage, thus effectively overriding any misinterpretation of the results from the chargers internal current sensor.
Note that I was using the 14.7V as an example as I don't know your alternator/redarc max charge voltage output.
But it's still relevant even if your redarc only puts out say 14V, as this voltage can lead to the same effect over longer periods, especially in the summer months, and if the charger lacks temperature compensation.

Hope this does make some sense to you.

Best regards, batteryvalue

AnswerID: 401979

Reply By: Member - Graham H (QLD) - Sunday, Jan 31, 2010 at 21:49

Sunday, Jan 31, 2010 at 21:49
Does he mean he has a REDARC isolator or a Redarc charger.

Why I ask is that he mentions charging the new one with a CTEK

I think he has a misinterpretation of technology here.

AnswerID: 401982

Follow Up By:- Monday, Feb 01, 2010 at 01:09

Monday, Feb 01, 2010 at 01:09
We don't know the answer yet Graham,

I just presumed it was a redarc charger he uses for onboard charging, and the ctek for mains charging.

Thinking about it, and reading Derek's comment it probably was an isolator.
But I don't think a defective isolator can lead to the described electrolyte boil off (which doesn't mean Dereks suggested test is moot).

I think his second battery has suffered internal cell shortage initially.
A shorted cell would lead to overcharge of the remaining cells, taking out one after the other, by electrolyte boil off and maybe even plate deformation and associated shorts due to increasingly high charging currents.
It's almost like a chain reaction, driven by the high current from the starter battery.
The current through the defective battery is really only limited by the line fuse, and the resistance of the wiring.
Was there even a line fuse on the defective battery?

This would explain the wet spots around the dead battery (boiling over of electrolyte).

Shorted cells are usually caused by shedding of active material under deep discharge conditions, in flooded designs. The stuff then piles up at the bottom of the container until it touches the electrodes which short out permanently. A real double whammy...

Has anyone ever noticed shorted cells in AGM batteries, which shows up as reduced terminal voltage (around 2V less).
In theory shedding can't happen with AGMs because the active material is held in place firmly by tightly packed glass fibre matting between the plates.

Best regards, batterymeister
FollowupID: 671430

Reply By: ABR - SIDEWINDER - Monday, Feb 01, 2010 at 00:49

Monday, Feb 01, 2010 at 00:49
Hi Mono

I think you are referring to the Redarc SBi12 isolator.

These like most isolators simply parallel the batteries when the engine is running and the cars alternator and regulator control the charge. The problem is that the Redarcs do burn their contacts and then the aux battery suffers a voltage drop from the isolator.

You will need to replace the battery as it sounds dead and beyond recovery, then do a load test on the Redarc.

To do this test discharge the new battery slightly with your fridge or other accessory. Then start the car. The Redarc should kick in and the red LED should come on. Now measure the voltage on each side of the Redarc and they should be very close, no more than 0.2V on a discharged battery.

If this test is good then perhaps the battery was just old and not well maintained, if not then you need a new Redarc.

I would also suggest you check all you connections and earths, especially those that have now been covered in acid.

Clean the acid off all paintwork and metal parts. Hot water and bicarb is good for this.


Derek from ABR

AnswerID: 402005

Follow Up By: ABR - SIDEWINDER - Monday, Feb 01, 2010 at 00:53

Monday, Feb 01, 2010 at 00:53
Note: 0.2V difference on Redarc terminals. This should be around 13.8V with engine running.
FollowupID: 671429

Follow Up By: mono2 - Monday, Feb 01, 2010 at 09:19

Monday, Feb 01, 2010 at 09:19
Thanks to everyone for your response, The info provided makes me a bit more informed on what to look out for (a big help to the non electrical type like me).
I will test my Redarc SBi12 isolator like Derek mentioned & hopefully it is just a case of a battery passed it life.
Once again Thanks to all for your help.
FollowupID: 671450

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