Deep cycle battery

Submitted: Sunday, Jan 12, 2020 at 20:02
ThreadID: 139551 Views:1286 Replies:6 FollowUps:23
What are people’s thoughts on fitting a deep cycle battery under the bonnet,
Would it get to hot .i have the main battery and a second heavy duty battery under the bonnet at present.

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Reply By: IvanTheTerrible - Sunday, Jan 12, 2020 at 20:12

Sunday, Jan 12, 2020 at 20:12
Deep cycle are OK under the bonnet. I've only ever had problems with AGMs under the bonnet due to heat
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Reply By: Allan B (Sunshine Coast) - Sunday, Jan 12, 2020 at 21:17

Sunday, Jan 12, 2020 at 21:17
Hi Kerry,

When you say "deep cycle" do you mean a Flooded battery or an Absorbed Glass Mat (AGM) battery?

Under the bonnet is not a good place for ANY battery. Flooded starter batteries survive reasonably and are placed there because it is convenient, but they would last longer if kept cooler. Much the same for deep cycle flooded batteries.
But the under-body heat kills AGM batteries every time. Heat shielding and cool air flow arrangements help but it is still better to place them elsewhere if possible.

If you are not sure whether your battery is flooded or AGM, please advise the battery brand and type as displayed on the battery label and we can help you.


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Reply By: Member - Bigfish - Sunday, Jan 12, 2020 at 21:36

Sunday, Jan 12, 2020 at 21:36
Some AGM manufacturers state that their batteries are ok to use under bonnet. SSB is one of them. They also make a stop/start battery that is agm and is used as a start battery with also able to be used as a deep cycle type. Heat can kill any battery and some people get years out of batteries and others do not. Bit like a lottery.
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Follow Up By: Allan B (Sunshine Coast) - Sunday, Jan 12, 2020 at 22:16

Sunday, Jan 12, 2020 at 22:16
Indeed SSB do allow their AGM's to be placed Under the bonnet, and still maintain warranty.

They speak of...."State-Of-The-Art Thermal Management System - Keeps battery cool during charging & general use making it better suited to hotter climates (like Australia’s top end) and under bonnet use."
I would love to know how they achieve that.


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Follow Up By: Bob Y. - Qld - Sunday, Jan 12, 2020 at 22:46

Sunday, Jan 12, 2020 at 22:46
Each battery thoroughly polished with Snake Oil, Allan, before they leave the factory?


Seen it all, Done it all.
Can't remember most of it.

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Follow Up By: Allan B (Sunshine Coast) - Sunday, Jan 12, 2020 at 22:50

Sunday, Jan 12, 2020 at 22:50
There's gotta be a catch!!

OK to place battery under bonnet.... just don't start the engine?

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Follow Up By: nats - Monday, Jan 13, 2020 at 03:00

Monday, Jan 13, 2020 at 03:00
I have had 2 SSB batteries in the engine bay of our Nissan Patrol for 3 years - one for starting and one for accessories. They are controlled by a system purchased and installed by ARB 10 years ago. A button in the cabin allows me to use both batteries to start the vehicle to ensure that the second battery is used a bit when we are not on a trip etc. I had them tested recently and they are both fine - the accessories battery was slightly more healthy than the starter one. I will replace them with the same batteries when I need to.
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Follow Up By: RMD - Monday, Jan 13, 2020 at 08:46

Monday, Jan 13, 2020 at 08:46
I, like Allan, are puzzled as to where the SSB battery Thermal Management System is. You buy one of their batteries, it looks like a battery, feels like a battery, works like a battery and is in fact a battery, That battery placed in an underbonnet location gets the same heating as any battery will receive in that location. SO, unless there is a physical insulation system and appropriate airflow the battery will get just as hot.
Many stop/start batteries do have insulation and some are at rear of engine bay too and still get engine bay heat, but may be protected slightly from direct radiant heat which will total any battery.
If said batteries are located at front of engine bay, then they are largely removed from the bay heat by having airflow almost directly to them before the engine bay. They must then run cooler. Usually people don't state WHERE the in the bay the batteries they have success with, actually are. Position makes a BIG difference to battery life. No one to my knowledge has taken battery temp readings of various UB locations and ambient temps to determine anything definite regarding battery life. So many variables, a simple recommendation from one person may be the battery killer for the one reading and asking for info because their fitting is an entirely different heat location..
Can the battery get cooled? Is it in the turbo radiant heat side? Is it insulated from direct radiant heat? Is it cushioned from vibration?, most are not.
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Follow Up By: Member - Bigfish - Monday, Jan 13, 2020 at 08:56

Monday, Jan 13, 2020 at 08:56
Maybe the external battery shell is of a different type of material. All batteries look like, feel like and act like batteries....yet internally (where we cannot see) they can be completely different. I know many of people have had good success with optima under the bonnet. Century/Yuasa also advertise an under bonnet agm. These under bonnet batteries are made from a different polypropylene material (normal batteries are ABS). Yuasa/Century are high quality, reliable batteries. The more heat resistant the outer casing the cooler the internals.

Maybe technology has caught up and agm can be used like any battery.

HEAT CAN KILL ANY BATTERY. I know plenty of people in top end who only get a couple of years out of batteries...others many years.
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Follow Up By: Member - shane r1 - Monday, Jan 13, 2020 at 09:07

Monday, Jan 13, 2020 at 09:07
Nats, you’ve had what I would consider a reasonable life out of those batteries. And they’re still going.
I know we would all love to get 5,6,7 or 8 years out of our batteries. But reality is most don’t. I’ve had long life out of some , and bloody short out of others. It’s a lottery.
I was told ( while I was in the retail industry) that batteries, are a grudge purchase. As in most people hate having to replace them . It’s true isn’t it?
But look at it like this in say three years , how many dollars worth of fuel , tyres etc do you put thru a vehicle . At the end of the day it’s a small part of the running cost.
I had this with farmers that would winge and complain about batteries. When they would be spending 50 to 100 grand on fuel, and a hell of a lot more on fertilisers and pesticide and herbicides. Their battery bill was pretty small in comparison!
It all about perception!
Cheers All
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Follow Up By: Mal58 - Monday, Jan 13, 2020 at 09:10

Monday, Jan 13, 2020 at 09:10
SSB warrant their AGM’s for 3 years and they say the batteries are designed to be used under the bonnet.

How they do it from a technical perspective, I don’t know.

I have had mine for 20 months and it seems to perform better than the marine deep cycle batteries that I have used in the past.

Time will of course tell.
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Follow Up By: Member - Lloyd M - Monday, Jan 13, 2020 at 09:20

Monday, Jan 13, 2020 at 09:20
I've had a Fullriver 120Ah AGM battery at the front under the bonnet of my 80 Series Toyota for 8 years next month, it is just showing its age now.

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Follow Up By: HKB Electronics - Monday, Jan 13, 2020 at 09:23

Monday, Jan 13, 2020 at 09:23
"The more heat resistant the outer casing the cooler the internals."

The casing may be heat resistant but that doesn't mean it offers good insulation properties to the internals, ie the plastic encapsulating semi conductors is virtually melt proof, heat it up it with a soldering iron it does not melt, however also has very good heat transfer properties heat up one end while holding the other and you will be quickly burnt by the heat transfer through the plastic.

I have recently installed a battery monitor to a Lithium dropin I have installed under bonnet, the temperature sensor is attached to the battery terminal so should give a reasonable picture of the internal battery temperature as the battery has a 3C current rating therefore a reasonable amount of copper connecting the post to the internals. Looking at the temperature of the battery through the day with the car garaged shows the ambient temperature. Monitoring the battery during a test drive showed the battery to get hotter than the environment but to be honest can't recall what it got up to. It was cooler than the engine bay but hotter than the environment. In my case the battery is mounted behind the headlight in a cool air stream away from heat sources apart from the radiator so for highway driving one would expect it to be cooler than the engine bay. For stop start driving eventually the battery will get to under bonnet temperatures, how long this takes will be more dependent on the mass of the internals than any likely insulation properties of a solid plastic case.

Bottom line is you would need a thick layer of insulation to stop heat getting into the battery, I have never seen any battery with internal insultation of any sort. Having a lot of lead inside the battery will slow the heat rise but eventually the internals will be the same temperature as the ambient or hotter.

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Follow Up By: Allan B (Sunshine Coast) - Monday, Jan 13, 2020 at 09:35

Monday, Jan 13, 2020 at 09:35

Certainly, premium batteries such as Optima are more durable but no battery enjoys heat. The cooler they are kept, the longer they will last.

On the subject of heat resistant battery cases I agree that some casing material would be more durable than others. However no insulation closely wrapped around a battery (or any other object for that matter) will keep it cooler unless cooling air is circulated between the insulation and the battery. All insulation will do is slow the transfer of heat through the insulation but with time the internals will reach the same temperature as the embracing environment.
Actually, in the case of a working battery, adding close insulation, whether it be casing or wrap, will increase the battery temperature because heat is being generated within the battery and needs to dissipate out to the environment to keep the battery temperature from rising.

Insulation can be used to shield engine heat provided that cooling air is circulated past the battery, as in my Troopy as per the photo below. Note that since that photo, the AGM battery has been relocated to the cabin. The heat shield remains to improve the environment for the cranking battery.


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Follow Up By: Peter_n_Margaret - Monday, Jan 13, 2020 at 09:48

Monday, Jan 13, 2020 at 09:48
I have recently replaced a still working 9 year old 120Ah Fullriver HGL standby battery that I have been using as a crank in the OKA.
I replaced it with an "unknown brand" AGM of similar size.
It is NOT under the bonnet.
Previous wet cell cranks in the same spot have lasted under 3 years. Killed by corrugations.
OKA196 motorhome
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Follow Up By: Allan B (Sunshine Coast) - Monday, Jan 13, 2020 at 10:03

Monday, Jan 13, 2020 at 10:03
Peter, 9 year battery life? Wow! There is no doubt that Fullriver are good.
I believe that corrugations have contributed greatly to the demise of my various under-bonnet batteries, both flooded cranking and AGM. The batteries were directly above the front wheel and the Troopy is not well known for a soft suspension! Heat was managed with the shield in the Followup above.
The AGM is now with its mate in the cabin approximately halfway between front and back axles so hopefully more comfortable. Simple physics now dictate half the shock intensity but double the frequency. Time will tell.

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Follow Up By: nats - Monday, Jan 13, 2020 at 11:14

Monday, Jan 13, 2020 at 11:14
Just a further point about my 2 three and a half year old SSB batteries : they have not had an easy life. We travel on the Len Beadell tracks every year and have done the Canning as well. The corrugations on those tracks are magnificent examples of their kind. We have no heat shield and the accessories battery is not far from the turbo. We run our Engel 40ltr. on freeze and store food in the Two Zone that sits atop the Engel so the second battery gets a belting. From my experience I don’t know what all the fuss is about having AGM batteries in the engine bay.
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Follow Up By: Member - David M (SA) - Monday, Jan 13, 2020 at 11:22

Monday, Jan 13, 2020 at 11:22
I always paint mine white before I install them for heat reflection.
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Follow Up By: CSeaJay - Monday, Jan 13, 2020 at 14:56

Monday, Jan 13, 2020 at 14:56

Fullrivers are good batteries but prone to heat damage; I suspect your particular placement and the exposure to heat in your OKA has a lot to do with it;

My Fullriver lasted 2.5 years under the bonnet of my 200 LC before it ballooned.
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Follow Up By: Member - Bigfish - Tuesday, Jan 14, 2020 at 07:21

Tuesday, Jan 14, 2020 at 07:21
CSeaJay...I dont think fullriver are any more prone to heat than the vast majority of batteries on the market. In actual fact they may be more tolerant.....reason I say this is because they are normally heavier (more lead on the internals) than most batteries advertised at the same or near amperage..
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Follow Up By: Alloy c/t - Wednesday, Jan 15, 2020 at 10:21

Wednesday, Jan 15, 2020 at 10:21
Heat versus batteries is an 'argument' of the likes of Toyota vs Nissan , BFG vs Coopers ..... Wifes Jeep , 2005 Turbo Diesel , hot as hell under bonnet , factory fitted Optima Red Top ,15 YEARS still going strong [yep heat kills batteries ] .... 90 amp hr Fullriver AGM bought August 2002 as an AUX , has been in 3 different vehicles 'under bonnet' , all turbo diesels [ no extra shielding done] , still going strong , part and parcel is to keep it 'simple' , no fancy expensive charging 'system' , a plain old smart solenoid and heavy thick wire .....
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Follow Up By: Member - Bigfish - Wednesday, Jan 15, 2020 at 10:51

Wednesday, Jan 15, 2020 at 10:51
You have been lucky...nothing more to it. For every story of a battery lasting 7-10 years there are dozens more telling of short life. Its ok for you as you drive a vehicle 15 years has come a long way. Smart systems are totally different to just chucking heavy gauge wire on and a simple solenoid. Obviously you dont agree with the fact that heat is a batteries greatest acknowledged by virtually every battery manufacturer, battery forum and the vast majority of off road forums. A lot also depends on what amperage and how often you are cycling the battery. So many variables between users. Heat versus batteries is absolutely nothing like ford vs holden. I,ve never seen anyone state that heat doesnt affect batteries...up until now!!!!
FollowupID: 904492

Follow Up By: Alloy c/t - Wednesday, Jan 15, 2020 at 11:05

Wednesday, Jan 15, 2020 at 11:05
Bigfish , perhaps you need to read up on the history of AGM batteries , originally designed for use in spacecraft , where extremes of HEAT followed by extreme COLD ......yes technology moves on , tell me why my old Nokia 101 mobile phone battery lasts 3x longer than my new beaut Apple ........
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Follow Up By: Member - Bigfish - Wednesday, Jan 15, 2020 at 11:47

Wednesday, Jan 15, 2020 at 11:47
Well Alloy I did look at the history and just as I thought you are wrong!!again!


The first lead-acid gel battery was invented by Elektrotechnische Fabrik Sonneberg in 1934.[6] The modern gel or VRLA battery was invented by Otto Jache of Sonnenschein in 1957.[7] The first AGM cell was the Cyclon, patented by Gates Rubber Corporation in 1972 and now produced by EnerSys.[8] The cyclon is a spiral-wound cell with thin lead foil electrodes. A number of manufacturers seized on the technology to implement it in cells with conventional flat plates. In the mid-1980s two UK companies, Chloride and Tungstone, simultaneously introduced 10 year life AGM batteries in capacities up to 400 Ah, stimulated by a British Telecom specification for batteries for support of new digital exchanges. In the same period, Gates acquired another UK company, Varley, specialising in aircraft and military batteries. Varley adapted the Cyclon lead foil technology to produce flat plate batteries with exceptional high rate output. These gained approval for a variety of aircraft including the BAe 125 and 146 business jets, the Harrier and its derivative the AV8B, and some F16 variants as the first alternatives to then standard nickel-cadmium (NiCd) batteries.

Every battery manufacturer also gives out the temperature range its batteries should operate at for longevity. All of them do not like heat!!

'Heat is a killer of all batteries, but high temperatures cannot always be avoided. This is the case with a battery inside a laptop, a starter battery under the hood of a car and stationary batteries in a tin shelter under the hot sun. As a guideline, each 8°C (15°F) rise in temperature cuts the life of a sealed lead acid battery in half. This means that a VRLA battery for stationary applications specified to last for 10 years at 25°C (77°F) would only live 5 years if continuously exposed to 33°C (92°F) and 30 months if kept at a constant desert temperature of 41°C (106°F). Once the battery is damaged by heat, the capacity cannot be restored.

According to the 2010 BCI Failure Mode Study, starter batteries have become more heat-resistant. In the 2000 study, a rise in temperature of 7°C (12°F) affected battery life by roughly one year; in 2010 the heat tolerance has been widened to 12°C (22°F). Other statistics reveal that in 1962, a starter battery lasted 34 months; technical improvements increased the life expectancy in 2000 to 41 months. In 2010, BCI reported an average age of 55 months for starter batteries, with the cooler North attaining 59 months and the warmer South 47 months. Colloquial evidence in 2015 revealed that a battery kept in the trunk of a car lasted one year longer than if positioned in the engine compartment.

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Follow Up By: Allan B (Sunshine Coast) - Wednesday, Jan 15, 2020 at 14:31

Wednesday, Jan 15, 2020 at 14:31

Alloy, lead-acid AGM batteries in "spacecraft"? I really don't think so mate.
Those things needed to actually lift-off the launcher.


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Reply By: Member - David M (SA) - Wednesday, Jan 15, 2020 at 11:30

Wednesday, Jan 15, 2020 at 11:30
Many years ago I accepted the fact that I was a 3year battery /60,000Km tyre
person. Life is so simply now.
AnswerID: 629531

Follow Up By: Allan B (Sunshine Coast) - Wednesday, Jan 15, 2020 at 11:33

Wednesday, Jan 15, 2020 at 11:33
Exactly Dave. No point in getting 'hot & bothered' about it, is there.


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Reply By: OzzieCruiser - Wednesday, Jan 15, 2020 at 12:54

Wednesday, Jan 15, 2020 at 12:54
A number of newer vehicles have AGM batteries as starter batteries living in the engine bay with no apparent issues.

The Discovery 4 changed to Varta AGM battery and is located in the same storage area as the older Varta Calcium battery and no extra shielding.
AnswerID: 629532

Reply By: Sigmund - Saturday, Jan 18, 2020 at 12:58

Saturday, Jan 18, 2020 at 12:58
Not all panels under the bonnet will take the weight without cracking, esp on corro.

Check the forum for your make/model for user experiences.
AnswerID: 629575

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