.....and another battery query

Submitted: Tuesday, May 28, 2013 at 13:53
ThreadID: 102459 Views:1825 Replies:5 FollowUps:9
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My previous 2 cars had a Remco agm battery as an auxiliary, one of them in the engine bay. Both worked great. With my current car (Prado 120 d4d) I allowed myself to be talked into a regular deep cycle battery after, not for the first time, being told that an agm won't be happy in the engine bay. Just over 2 years on, the thing has died on me after repeatedly going powdery white (calcifying?) around the terminals. My latest advice is that it had been regularly charging and not used enough, therefore overcharging. My question is; why hasn't this been a problem previously. I use it just the same, with occasional camping throughout the year. Also, what can I do to stop it "overcharging", if it is actually doing that. Maybe run a gadget off it to use some energy?
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Reply By: MEMBER - Darian, SA - Tuesday, May 28, 2013 at 14:17

Tuesday, May 28, 2013 at 14:17
Can't comment on your main query - I'm sure the regular autosparkers here can help, but ............as an aside, one major battery manufacturer will not warrant their AGM's if installed in an engine bay. I chose a flooded DC for my engine bay aux - it has less resistance to vibration when compared to the AGM but that is not a problem for me. For harsh vibration conditions (eg. corrugations form hell), an AGM installed elsewhere is probably the go.
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Follow Up By: Steve M1 (NSW) - Tuesday, May 28, 2013 at 17:18

Tuesday, May 28, 2013 at 17:18
I was on a website the other day and it listed and described various batteries. I was looking at the Fullriver and it clearly said that it was an agm yet suitable for the engine bay. It stood out because it flies in the face of the general consensus that this is not the case. I suppose there's always the possibility that this supplier might have nit wrong. Perhaps somebody is aware of it?
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Reply By: Member - Frank P (NSW) - Tuesday, May 28, 2013 at 15:32

Tuesday, May 28, 2013 at 15:32
I have the same vehicle as you, Steve. The Prados alternator output is too low to properly maintain an aux battery, IMO. It is down around 13.1V; I see that constantly on my Scangauge.

I have a wet calcium dual purpose aux battery (Supercharge Allrounder) under the bonnet behind the rh headlight. It needs 15.6V in absorption phase before going to float- way beyond what the Prado puts out. I use a dc-dc charger to provide the correct charging profile for that battery. It is temperature compensated and also automatically cuts out if the battery temp gets over 50 degC. Bloody inconvenient sometimes, but saves cooking the battery. Battery is 4 yearrs old and still seems to be going ok. It gets light duty, though, so that may contribute to its long life.


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Follow Up By: Member - Phil G (SA) - Tuesday, May 28, 2013 at 17:04

Tuesday, May 28, 2013 at 17:04
Gday Frank,
I have a scangauge too - the voltage reading on it is not accurate - most times it underreads by the best part of 0.3V. That's comparing it to an accurate digital voltmeter reading off the battery terminals. So if yours is anything like mine, when your scangauge says 13.1V, the battery voltage is most likely 13.4V.
Great device otherwise.

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Follow Up By: Steve M1 (NSW) - Tuesday, May 28, 2013 at 17:38

Tuesday, May 28, 2013 at 17:38
ha - I had the voltage at 13.2. Anyway, not really enough. I am looking into the dc dc solution. Is this a ...erm.... "current" (pun intended) trend with modern cars? I take other vehicles have the same issues? I might also add, my previous fridge was a waeco, which was less demanding and I had not issues with it, so I'm wondering if it's the Engel with it's heavier demand. It has been suggested that it doesn't take much to stop them working if supply isn't all it should be.
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Follow Up By: Member - Frank P (NSW) - Tuesday, May 28, 2013 at 19:26

Tuesday, May 28, 2013 at 19:26
Hi Phil,
Very interesting comment. I would have thought that the OBDC codes as interpreted by Scangauge would have been pretty accurate. But I suppose it's all in the interpretation as coded by Scangauge's engineers. I'll check mine tomorrow.

In any case IMO, from what I have read and studied, 13.4V is still not enough to do the job properly for an aux battery where you probably want the max depth of charge, and it's a compromise even for a crank battery.


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Follow Up By: Member - Phil G (SA) - Tuesday, May 28, 2013 at 20:05

Tuesday, May 28, 2013 at 20:05
Gday Frank,
I run a separate voltage measuring wire at each battery and hook them up to a decent voltmeter inside the car so I get an accurate reading at each battery and know what's happening. I was surprised at how much the scangauge was out, and I expect its because its reading voltage from the same tiny wire that is drawing current for the unit or supplying the ECU.

The optimal charging voltage of a battery varies with temperature - the warmer the environment, the lower the required voltage. So lower voltage under the bonnet is appropriate. Mine starts at 14.15V when cold and settles at about 13.5 when the motor is hot. My voltage also varies with revs - at 500rpm idle it usually reads lower than at 1500rpm so if you're measuring voltage, do so when the vehicle is driving. As far as the cranking battery goes I think that's all OK on most vehicles.

Problem with auxillary batteries is that if the battery is installed in a cooler environment (eg in trailer or back of car) the temperature regulation is no longer appropriate. But an auxillary under the bonnet usually charges up OK if given enough time. The wet cell deep cycle batteries are usually Calcium-Calcium and need higher charge voltages and don't charge well with the low vehicle voltages. They need to be topped up via a Dc-dc on the move or conventional charger at home. Thats why I use a hybrid battery (eg Exide Extreme, Overlander or marine battery) as my auxillary.
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Reply By: Member -Dodger - Tuesday, May 28, 2013 at 16:32

Tuesday, May 28, 2013 at 16:32
The Prado alternator has a low charging regime so will not really charge a battery to its full extent.
There is an aftermarket chip type fuse that is available for the Prado that lifts the charging voltage for the battery.

.See Here.

I used to have a handle on life, but it broke.

Cheers Dodg.

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Follow Up By: Steve M1 (NSW) - Tuesday, May 28, 2013 at 17:29

Tuesday, May 28, 2013 at 17:29
yeah Dodge, I've heard about those diode boosters but am a bit reluctant at this stage until I've got my head around it.
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Reply By: Member - Rosco from way back - Tuesday, May 28, 2013 at 16:49

Tuesday, May 28, 2013 at 16:49

The response regarding "overcharging" sounds a little suss to me.
How come it's not overcharging your main battery? That's the job of the voltage regulator to ensure the charging stops when the battery gets to a certain voltage.
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Follow Up By: Steve M1 (NSW) - Tuesday, May 28, 2013 at 17:14

Tuesday, May 28, 2013 at 17:14
That's what threw me. On the one hand, the alternator only has sufficient charge for the main battery yet this guy reckoned because I wasn't utilising the aux batt it just kept absorbing charge and was therefore overcharging. To be fair, he hadn't had a good look at it and suggested I book it in but he doesn't sound like he is across these issues. I think we get auto sparks that are decent enough in the general area but they often don't understand the applications.
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Follow Up By: Member - Frank P (NSW) - Tuesday, May 28, 2013 at 19:39

Tuesday, May 28, 2013 at 19:39
I very much doubt that your (and my) Prado with an alternator output at 13.1 to 13.4 could overcharge any lead-acid battery. More likely that a typical aux battery will always be undercharged to an extent, resulting in sulphation and reduced calendar life.

If I were you I' d go down the path of a dc-dc charger for your second battery. I think you will need to choose the battery and charger combination because not all dc-dc chargers can provide the ideal output for all batteries. A fully programmable one such as a Ranox (sadly, no longer avaiable) can. Most others have switch settings which are usually close to required settings but not bang-on, depending on the battery.

Choose a battery and dc-dc charger combo that will live happily together.


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Reply By: Member - J&R - Tuesday, May 28, 2013 at 20:04

Tuesday, May 28, 2013 at 20:04
A Scangauge will not give you accurate system voltages, especially alternator charging voltage and battery voltage.
The only way to accurately check them is with a correctly calibrated voltmeter at the alternator and at the battery. Ignition/ecu voltages are not accurate indicators of charging rate. This is dependant on may things, incl battery condition, rest time, startup charging sequence etc. I hope you get the idea. In late model cars there are a nightmare to test accurately. And impossible to do without detailed knowledge. (and by the way, it will only be far worse with the next generation of cars with hybrid and semi intelligent control systems.)

The 'powdery white' is terminal corrosion. Air acts with the acid spills/vapour and the terminals. Most usually on the positive terminal.

If it hasn't been a problem previously, perhaps something has changed....

Have it tested by a reliable Auto Electrician familiar with aux battery systems and the modern latent/lazy charging systems in late model cars.

There are many experts on forums such as this one, and some even know what they're talking about. Most do not. Talk to an expert or you will end up spending money chasing your tail, and replacing/fitting equipment you don't need.

Let me know where you are via private message and I'll point you to a good one.
AnswerID: 512038

Follow Up By: Steve M1 (NSW) - Tuesday, May 28, 2013 at 20:45

Tuesday, May 28, 2013 at 20:45
thanks mate - pm sent

just when you begin to get you head around this stuff they move the bloody goal posts
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