AGM batteries under the bonnet

Submitted: Saturday, Mar 08, 2014 at 16:11
ThreadID: 106611 Views:13717 Replies:12 FollowUps:15
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Hi,
I need to replace my main battery in my 2009 D Max. It is currently a lead acid type and I was wondering if a AGM battery would be able to do the job and be able to handle the heat of the engine bay.
Has anyone had any experience?
I have a AGM as my DC battery for the fridge and lights that is in my tray.
Dave
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Reply By: Member - Tony H (touring oz) - Saturday, Mar 08, 2014 at 16:47

Saturday, Mar 08, 2014 at 16:47
Hi Dave,
If you do a search on this subject I think you will find that AGM batteries don't like under bonnet heat.
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Reply By: Tony F8 - Saturday, Mar 08, 2014 at 17:34

Saturday, Mar 08, 2014 at 17:34
David,
I have had agm's (2 to be exact approx 8 years per battery)under the bonnet as auxiliary's in the 80 series for over 16 years and never had a problem. I have read on the forum about agm's frying themselves, well I think it's a load of BS. They are are commercially manufactured battery, no different to a lead acid in case construction. The first was a trojan and the second a fullriver, and again never had a problem with either of them. Unless it's sitting right beside your exhaust you would not have a problem, do you see the insulation on wiring under the bonnet melting, no so why would a battery mounted at the front of the engine bay get any hotter than wiring running across the firewall. This is not meant to sound aggressive, but some of the hearsay stories that you occasionally read on here are unqualified waffle.
Drive safe.
Tony F8
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Follow Up By: Dennis Ellery - Saturday, Mar 08, 2014 at 19:02

Saturday, Mar 08, 2014 at 19:02
Here is a bit more of unqualified waffle.
An associate of mine gets 2 to 3 years out of AGMs as a starter under his bonnet - another tells me he has got 15 years out of an Optima. It’s hard to sort the wheat from the chaff.
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Follow Up By: Allan B (Member, SunCoast) - Saturday, Mar 08, 2014 at 19:18

Saturday, Mar 08, 2014 at 19:18
From "Battery University" site:
"AGM and other sealed batteries do not like heat and should be installed away from the engine compartment. Manufacturers recommend halting charge if the battery core reaches 49°C (120°F)."

From the Trojan site:
"The higher the battery temperature, the faster chemical reactions will occur....higher temperatures... will result in a corresponding loss of battery life. Heat is an enemy of all lead acid batteries, FLA, AGM and gel alike and even small increases in temperature will have a major influence on battery life."

From the Exide site:
"Heat is the number one killer of a battery.... life is drastically reduced over time."

Cheers
Allan

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Follow Up By: John and Regina M - Saturday, Mar 08, 2014 at 19:21

Saturday, Mar 08, 2014 at 19:21
Oh I see.
You're comparing the wiring insulation with the case of the battery. Hmmmm.

So how about the rest of the components? Electrolyte? Plates?
The chemical process that takes place inside the battery?

However you have done well. But let's not get ahead of ourselves. One good luck story does not a standard set.
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Follow Up By: Member - John and Val - Saturday, Mar 08, 2014 at 19:33

Saturday, Mar 08, 2014 at 19:33
Tony - I agree there's sometimes a bit of bs regarding electrical stuff... and it certainly can start battles!

But temperatures under the bonnet, especially near the exhaust can get hot. Century Yuasu Batteries spec their AGMs to handle up to 50 degrees C when discharging, 40 degree when charging. That's a long way below the melting point of plastic insulation!

As you say, the exhaust is the problem area. I've seen installations where an insulated panel is fitted between exhaust and battery. Good idea.

Simple fact is that it's better not to expose AGM (and especially gel) batteries to under bonnet temperatures. If you must, you must, but provide protection from radiant heating by the exhaust system.

Cheers

John
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Follow Up By: Bob Y. - Qld - Saturday, Mar 08, 2014 at 20:02

Saturday, Mar 08, 2014 at 20:02
Don't think 80 series are a good example for using AGM's under the bonnet. Batteries are at the front of the engine bay, and well protected from excessive heat.

The 2H engined 75 series, for example, were flat out getting 12 months out of a lead acid battery.

Bob.

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Can't remember most of it.

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Follow Up By: Tony F8 - Saturday, Mar 08, 2014 at 21:59

Saturday, Mar 08, 2014 at 21:59
Just following up on replies to the thread.

Exide Batteries, Exide Australian made batteries have been designed to withstand the high under bonnet temperatures and excessive vibration experienced by motorists.
Trojan Batteries. The warranty is rendered void if the battery becomes unserviceable due to fire, wreckage, FREEZING, neglect, abuse, damage or act of God.
I apologise if practical expirience is not as valuable as the written word, I did state it was a 80 series in my experience, and have read the exerts from the battery university, but reading the warranties of battery manufacturers if you dont torque wrench the clamps to a specific kn, you will void the warranty. I have numerous friends that have agm's under the bonnet and have had no reduction of their battery life.I respect the opinions of other contributers on this site, even when some ride a very high horse.
Drive safe.
Tony F8.
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Follow Up By: Dennis Ellery - Saturday, Mar 08, 2014 at 22:27

Saturday, Mar 08, 2014 at 22:27
Hi Tony - don't take offence
It’s impossible to accurately compare the duty cycles, loads, temperature of battery’s location, float voltages on standby, and battery life etc on a forum like this.
Obviously you are doing the right things to get a good life out of your batteries.
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Follow Up By: Member Andys Adventures - Sunday, Mar 09, 2014 at 09:28

Sunday, Mar 09, 2014 at 09:28
I put an optima battery in my New Triton 3 years ago and had no troubles with it and I drive in the hottest parts of Australia. Been in there since new and has never let me down. Saying that the acid one is still going strong pumping fuel and gets recharged ever other day.
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Reply By: Dennis Ellery - Saturday, Mar 08, 2014 at 18:38

Saturday, Mar 08, 2014 at 18:38
My 4WD under bonnet temperature is around 80 deg and the electrolyte gets above 65 deg.
As such I use marine batteries – the flooded maintainable type.
Many manufacturers won’t guarantee AGMs in these temperatures.
My vehicle is a V8 diesel and it may run hotter than yours – put a couple of old beer cans of water under the bonnet, and measure their temperatures after you take an hour or so journey – it may help your decision.
AnswerID: 527911

Follow Up By: Ross M - Saturday, Mar 08, 2014 at 19:25

Saturday, Mar 08, 2014 at 19:25
Use full beer cans and then drink them for a definite on the heat the battery is feeling.
An AGM in a Dmax bay will still get too hot for good life.
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Follow Up By: Dennis Ellery - Saturday, Mar 08, 2014 at 21:45

Saturday, Mar 08, 2014 at 21:45
Ross you are talking to a beer connoisseur -if it’s above zero it’s too hot to drink.
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Reply By: Allan B (Member, SunCoast) - Saturday, Mar 08, 2014 at 20:15

Saturday, Mar 08, 2014 at 20:15
Regarding engine bay temperatures, Thread 91116 has some temperature measurements taken after I fitted a battery heat shield in the Troopy.
68c on a 30c ambient day and not driving hard. The shield reduced the battery section to 48c. Better but still high for AGM's. And the exhaust is on the other side from the batteries.


Cheers
Allan

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Follow Up By: Dennis Ellery - Saturday, Mar 08, 2014 at 21:12

Saturday, Mar 08, 2014 at 21:12
Allan you’ve done well.
I’ve got an exhaust either side and there is not a nat’s whisker of room to fit an insulation barrier.
Even some flooded batteries don’t like the rear position under my bonnet – I had a flooded deep cycle (lead antinomy) which boiled itself to death in that position. My best solution is flooded marine batteries for deep cycle in hot spots.
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Reply By: MEMBER - Darian, SA - Saturday, Mar 08, 2014 at 20:34

Saturday, Mar 08, 2014 at 20:34
Just as a point for consideration...... the last time I looked, Century for one were still stating that they will not warrant any of their AGM's installed under bonnet.
AnswerID: 527916

Reply By: David M28 - Saturday, Mar 08, 2014 at 20:44

Saturday, Mar 08, 2014 at 20:44
Thanks for all your help and so quickly. You have help make up my mind. I was told by a young lad in the 12volt shop, but wanted some advice from the real world from experienced people that have tried and tested the things.

See you all off the beaten track, hopefully not with a dead battery.
Dave

AnswerID: 527918

Follow Up By: Stevo - Tuesday, Mar 11, 2014 at 12:56

Tuesday, Mar 11, 2014 at 12:56
What brand of AGM battery are you considering Dave?
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Reply By: chisel - Saturday, Mar 08, 2014 at 20:53

Saturday, Mar 08, 2014 at 20:53
Some AGMs are rated for under bonnet use and come with a warranty covering that.
AnswerID: 527920

Follow Up By: Dennis Ellery - Saturday, Mar 08, 2014 at 21:40

Saturday, Mar 08, 2014 at 21:40
Yes that’s correct for high quality, low resistance batteries – their cost is pretty high.
I use a Lifeline AGM deep cycle in my caravan - about twice the cost of a standard AGM but over twice the life plus greater DOD and fast charging ability.
They also make AGM starter batteries, which they guarantee under the bonnet – two to three times the cost of a flooded cell – I was tempted to try one but I would need to get about 10 years out of it to justify the expense, so I stuck with flooded marine.
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Reply By: Member - Des Lexic - Saturday, Mar 08, 2014 at 22:13

Saturday, Mar 08, 2014 at 22:13
I also had an AGM Fullriver battery located at the front of the engine bay and i was dissapointed to only get 8 years out of the battery. It' a diesel 100 series too. When i replaced it, i was able to get some foil backed rubber sheeting so that i could fit it on the engine side to give some extra insulation. In 7.5 years, i will see if it worked.
AnswerID: 527924

Reply By: Phil D1 - Saturday, Mar 08, 2014 at 22:23

Saturday, Mar 08, 2014 at 22:23
I have used AGM batteries under the bonnet of my 100 series 1HZ with aftermarket turbo and inter cooler , so it gets hot. Some brands have not lasted well but I am finding SSB batteries are doing well as they have a higher temp rating.
AnswerID: 527927

Reply By: The Bantam - Saturday, Mar 08, 2014 at 22:24

Saturday, Mar 08, 2014 at 22:24
The first and most important thing to understand is that many generalisations concerning batteries...especially AGM are unreliable.

The various manufacturers fiddle with this and that and in current times can produce a wide range of performance options from batteries.

There ARE AGM batteries that are specifically designed as cranking batteries and to cope with reasonable under bonnet temperatures.

BUT and the is a BIG BUT......you must consult the specifications and application recommendations of the individual battery model involved.

Some popular AGM batteries on the market have very poor high temperature tollerance indeed....in fact a couple of popular AGM models would be out of spec sitting under a shady tree in some of our hotter areas.

There are a lot of people spending big on AGM and getting nothing but short life and disapointment from them...because they have not consulted the manufacturer information.

One question I ask......IS why AGM...serioulsy WHY.....do you realy want to pay twice as much as you need to for a battery and very likley get no advantage.


ALL the technology used in AGM is available in flodded batteries thesed days.


The single biggest difference that typically ( remember what I said about generalisatons) makes flooded batteries more tolerant of heat than AGM is that the fluid in the flooded battery allows it to disipate heat better to the case than a battery that has had all the free fluid tipped out (AGM).

A good quality sealed marine battery will give you most of the advantages of AGM, with far better heat tolerance and at half the price.

Personally I like the Supercharge Seamaster Gold...as far as i know it is the only sealed maintenance free lead acid battery that can easily be topped up.
Once out of warranty, you can peel the top sticker off to reveal the vent valves which screw out like a conventional screw top battery.

If you still have your heart set on AGM...know your business and read and understand the specification sheets and application recommendations in detail before buying.

Cheers
AnswerID: 527928

Follow Up By: The Bantam - Saturday, Mar 08, 2014 at 22:28

Saturday, Mar 08, 2014 at 22:28
OH BTW..under the bonnet is the worst place to fit any battery if you want the best service life.

AND temperature above 25C will reduce the service life of ANY lead acid battery...the hotter the more it will reduce its life.

cheers
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Reply By: nickoff - Sunday, Mar 09, 2014 at 09:27

Sunday, Mar 09, 2014 at 09:27
I Live in the Top End of Australia.

Under bonnet battery life is very short.

Best I've ever got was still less than 3 & 1/2 Years. Normally need to replace just over 2 years.

Experience in both petrol/gas, and diesel vehicles, cars and utes.

High ambient temperatures shorten battery life signicantly.
AnswerID: 527950

Follow Up By: grey yesmad - Tuesday, Mar 11, 2014 at 23:05

Tuesday, Mar 11, 2014 at 23:05
both my ctek chargers (240-12 and dc-dc) have a heat sensing probe to monitor the battery temp. when charging and react accordingly to high temperatures. There must be a reason for not charging when the battery is over a certain temperature??

my 5 amps worth
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Reply By: Member - bungarra (WA) - Wednesday, Mar 12, 2014 at 12:11

Wednesday, Mar 12, 2014 at 12:11
I have had two AGM batteries under bonnet (LC 79 series) and both only a few years life.

Now fitted a Marine grade as well as a DC DC Ctek dual charger. The temp sensor for this charger is alongside the battery terminal on the aux battery..........the charger will never allow charge to the battery when engine is running..... as always a warning that it is over temp!

That tells me its too damn hot at the rear of the engine bay...........so I now I use the solar option when stationary and a Diode to increase the charge voltage from the OE battery at the front of the engine bay to the aux battery at the rear....time will tell I guess

12v shop?.........well I don't listen to them any more
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