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AGM is fine under bonnet of a turbo GQ diesel

  • Yes (I have one and no issues)

    Votes: 4 40.0%
  • No (I tried and failed)

    Votes: 2 20.0%
  • Unsure (I have not tried but heard of problems)

    Votes: 4 40.0%
  • Maybe (I have not tried but head you can)

    Votes: 0 0.0%
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Discussion Starter #1
Hey guys

I see lots of posts with pro's and con's as to should you run an AGM Deepcycle under the bonnet on at GQ (or any 4wd) as a 2nd battery.

Warranty aside, it would be great if you can vote on this to tell me who has had issues and who has not with heat and batteries 'exploding/buldging/leaking'

Usage aside, I am only interested in the 'heat' and 'longevity' issue.

Thanks!
 

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From what I understand the physical characteristics of the AGMs are suited to our primary and secondary battery needs, i.e. starting battery and a second battery. However, I read that AGMs need a minimum of 14.2 volts electrical pressure to recharge them during normal use and none of my vehicles charge that high. Less than 14.2 volts will result in a constantly undercharged battery, sulfation and premature failure. Now if a AGM battery has the potential to thermal runaway like a nicad then it could explode causing lots of damage. Considering the cost of an AGM I am not convinced to go that route yet.

Perhaps someone with more knowledge experience could jump in.
 

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Sealed AGM batteries that are designed for constant charge, not too much heat as UPS systems are not suitable under the bonnet and I have seen a few in camper trailers that have bulged from charging heat.

But AGM batteries like Optima are meant for under car/truck bonnets and take extreme abuse compared to the other types of batteries.
 

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Charging damage is from improper charging, the use of cheap chargers or the wrong mode selected on the charger. You cannot use a cheap "trickle" charger to constantly maintain a battery without farking it.
 

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i have an AGM designed for UPS use under the bonnet in my ute, its my cranking battery and i have not had a problem with it. I do normally have it on float charge while its sitting with no use.
 

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Hi foodie, being as your planning on putting an auxiliary battery under the bonnet, why are going with an AGM.

A standard flooded wet cell battery is specifically designed to tolerate the harsh conditions of under bonnet mounting, they cost less and will probably last as long if not longer than an AGM will.
 

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I had a a battery place tell me that they don't like the heat in the engine bay, and that a wet cell was a better option. I was not buying one off them either, so it was not a biased opinion.
 

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Hmmmmmm seems some of the info I have read is erroneous and confusing. AGMs do not tolerate high charging voltages......

More feedback needed.
 

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Hi Twinotter, Spiral Wound automotive grade AGMs, like Optima, will work fine under the bonnet.

The problem is that most AGMs in RV use are NOT Spiral Wound but are Flat Plat, like Fullriver.

Flat Plat AGMs must not be charged with voltages higher than 14.4v ( and here is the problem ) AT ROOM TEMPERATURES. As the battery’s temperature goes up, the charge voltage level must come down.

Flat Plat AGMs also have a limit on the amount of charge current they can tolerate, and this is some where between 20% and 30% of the total Ah. This means, if you have a 100 Ah Fullriver, the maximum current you can charge them with is around 25 amps AT ROOM TEMPERATURE.

By putting a Flat Plat AGM under the bonnet, you subject the battery to high temperatures, high charge voltages and high charge currents and this combination is lethal to Flat Plate AGMs.

In many cases, it will take a while to damage the battery as long as the AGM is not discharged to low. The instant you have a low charged AGM, you will exceed all it’s safety perimeters when you start your motor and this is when they are damaged big time and when you often see the football effect.
 

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Hmmmm, very interesting. My rigs are 24 volt Safaris (2 12 volts in series). Optimas are proven not to work well in this configuration due to battery balancing. Seems hard to justify Flat plate AGMs for my use.
 

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Hi Twinotter, I can’t comment on Optima batteries used in series, I’ve never had anything to do with any AGMs in series as crankers. All my experience with batteries in series for cranking batteries have been with flooded wet cells.

In your case I would imagine flat plate AGMs in series would only be good in a house battery array.
 
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