AGM batteries under the bonnet

Hi Dave,
If you do a search on this subject I think you will find that AGM batteries don't like under bonnet heat.

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

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.

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.

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.

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

Some AGMs are rated for under bonnet use and come with a warranty covering that.

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.

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.

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

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.

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