AGM Sealed Battery under the bonnet

Submitted: Tuesday, Jun 14, 2005 at 21:19
ThreadID: 23871 Views:3373 Replies:10 FollowUps:1
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Has anyone used AGM's under the bonnet? I have dual batteries, one for cranking and one for the fridge, but I am told AGM's don't like it hot..

Is insulating it the way to go? Or putting them in the back? I have a REMCO 100a/h SLA AGM, the specs don't go above 40 degrees, it gets ALOT hotter than that under the bonnet, espessially in the desert...

Any ideas would be very much appreciated.

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Reply By: Member - Jimbo (VIC) - Tuesday, Jun 14, 2005 at 21:29

Tuesday, Jun 14, 2005 at 21:29
Not sure Viking,

I've had an AGM in the back of the car for a year and it works well.

My only suggestion is to contact the chap at Federal Batteries in Sydney, great advice from him.


AnswerID: 115786

Reply By: Steve - Tuesday, Jun 14, 2005 at 21:51

Tuesday, Jun 14, 2005 at 21:51
my chap...also in Sydney says AGM's under bonnet are a NO-No...don't like to be cooked and work best when cooler rather than hotter...under 80 series bonnet in outback conditions does not qualify for the recommended it was wet cells all the way...and not as many A/H's as i would like to take get a solar panel to keep up with the comsumption of fridges etc !! expensive alternative ..but maybe the only one outside buying one of those damned genny's that rent the air in the oddest of places and spoil life for everyone else within cooee...
AnswerID: 115789

Follow Up By: Viking66 - Tuesday, Jun 14, 2005 at 21:56

Tuesday, Jun 14, 2005 at 21:56
Steve, thanks for the tip, I just cant get a straight answer from the battery folks, some say no problem at all, others say no, the specs on the AGMs say "more heat resistant to wet cells", but then don't talk about temps above 40 celcius, whats that all about....

FollowupID: 371382

Reply By: Steve - Tuesday, Jun 14, 2005 at 22:15

Tuesday, Jun 14, 2005 at 22:15
From my experience: listening to the folk on the ground that do the instalations and sign off on a job, are far more important to me than all the printed crap and horsebleepthat these companies put out ..especially if they make their product overseas..aka ...PRC and similar...not that they all make rubbish..but my man on the ground expects me to come back as a loyal I presume he wants by business..pieces of paper promising the earth ...go out on the dunny nail...
AnswerID: 115791

Reply By: Alloy c/t - Wednesday, Jun 15, 2005 at 07:37

Wednesday, Jun 15, 2005 at 07:37
Have got 2x 80amp fullriver agm under bonnet of 80series turbo diesel , 1 as starting ,other as aux thru rotronics , allso 3x 80amp fullriver agm on c/trailer , no problem under bonnet or in c/t , excessive heat will shorten ANY batterys life , LESS so with agm as no liquid loss due to heat ,your regular underbonnet temp is allready 2x/4x higher than any desert temp , invest in the AGM ,you wont regret the purchase.
AnswerID: 115819

Reply By: Sand Man (SA) - Wednesday, Jun 15, 2005 at 08:07

Wednesday, Jun 15, 2005 at 08:07
Yep, agree with Alloy.

I also run an AGM auxilliary (Exide Orbital) and have no trouble with it at all in the Engine compartment.

The sole reason for installing the Orbital is because the battery is located at the back of the engine bay against the fire wall, it was difficult to check the electrolyte level in the previous wet cell battery without resorting to a step ladder.

The Orbital (or any other AGM) doesn't have this problem so it was a no brainer.

If the heat is extreme in your vehicle, regardless of what battery you have installed, try a barrier of some sort (e.g. a piece of ally plate) between the battery and engine/exhaust manifold to reduce radiant heat.

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AnswerID: 115824

Reply By: Marko - Wednesday, Jun 15, 2005 at 09:03

Wednesday, Jun 15, 2005 at 09:03
G'day Viking,

I recently installed dual batteries on the 80 series. Used an AGM battery as an auxilliary under the bonnet and it hasn't missed a beat. I have a voltage meter installed and it was fine during the summer and the 10 days in the Flinders in March.

AnswerID: 115831

Reply By: Outbacktourer - Wednesday, Jun 15, 2005 at 09:26

Wednesday, Jun 15, 2005 at 09:26
I've got a small Odyssey mounted just to the front and side of the extractors in a race car and it's into it's 5th year...also survived a shunt that jammed it up against the alternator but only left a small ding in the metal case.
AnswerID: 115835

Reply By: Mike Harding - Wednesday, Jun 15, 2005 at 19:18

Wednesday, Jun 15, 2005 at 19:18
Fullriver (who another poster mentioned) quote a maximum operating temperature for their AGM batteries of 50 deg C - to quote from their data sheet:

2) Batteries operate on electrochemical reaction which
converts chemical energy to electric energy. The
electrochemical reaction is reduced as the temperature lowers,
thus, available discharge capacity is greatly reduced at
temperatures as low as 5°F (-15°C). For the high temperature
side, on the other hand, the discharge temperature should not
exceed 122°F (50°C) in order to prevent deformation of resin
materials which house the battery or deterioration of service

Underbonnet temperatures will probably reach well in excess of 50C I imagine the effect of this would be to shorten the life of the battery.

Mike Harding
AnswerID: 115910

Reply By: Member - Collyn R (WA) - Sunday, Jun 19, 2005 at 11:47

Sunday, Jun 19, 2005 at 11:47
Underbonnet temperatures are not as high as many people think (excepting directly above a turbo or non-turbo exhaust manifold) whilst driving at normal speeds.

They do however build up within seconds immediately after stopping but this presents no problem if the engine is not running and thus the battery is not charging. There may however be serious heat build up in hot city areas where the engine may be idling for long periods. Most failures seem related to the latter situation.

The problem is thermal runaway ie., - a battery accepts a charge more readily when it is hot, and as a vehicle alternator is a constant voltage system, the charge rate increases. This in turn adds heat to the battery, which then causes it to accept even more charge - and so on. It's a sort of non-nuclear melt-down.

Most AGMs require a lower than normal float voltage (typically 13.2 volts). It is best not to float charge for long periods - ie when the vehicle is unused for a month or two. It is not necessary anyway as AGMs have very low internal loss.

If using an AGM as an auxiliary battery in the above adverse situations it would probably pay to have a master charging switch that disconnects it from the charging system. Once fully charged it stays that way for the better part of a year anyway!
Collyn Rivers
AnswerID: 116353

Reply By: Viking66 - Monday, Jun 20, 2005 at 21:19

Monday, Jun 20, 2005 at 21:19
Thanks for all of your posts guys. awsome.

I have put one AGM under the bonnet and the other up the back, saves me 30kgs up the back. I will put a heat shield on it next week, as it is neat the turbo. It only gets warm through town so far, but in the desert it will get hot.


AnswerID: 116615

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