AGM Batteries, especially cheap nice cost effective Chinese ones don’t like heat too much. All Lead Acid batteries are subject to thermal runaway when charging and the design of an AGM is such that as it gets closer to fully charged the catalyst effect that stops it losing water produces plenty of additional heat.
The AGM construction has approximately 50% more lead in it than a normal flooded cell, and the electrolyte is not free to move around as easily as it charges. The cells are tightly packed with an adsorbent wadding leaving no room for movement.
If you overcharge an AGM or overheat it, it will bulge the top and sides. If the bulging becomes bad enough, the battery will fail. Optima tries to stop this problem by winding their plates in a spiral, a stronger construction. Odyssey tries to stop it by placing a metal jacket around the battery.
Finally, a batteries life is defined not only by how heavily it’s used, but also by what temperature it’s used at.
So when I fitted AGM’s to my cruiser, I knew heat may be an issue.
The 80 Series cruisers came with a battery heat shield, as do Falcon’s and many other vehicles. Heat reduces a battery lifespan significantly, from 10 years to 2 or less.
I found the majority of the heat was from the radiator fan blowing onto the batteries. Due to the placement of the engine, much of the hot air goes straight to the batteries. I measured battery temps of over 65c.
Now with the heatshields they don’t get over 40c, even after several hours of driving. Fast or slow doesn’t seem to matter too much.
I had two of the aluminium ones folded up and I trimmed them to size with a nibbler. I only had time to fit one before my last trip and quickly made up a temporary shield from a windshield sun reflector for the other. Both work equally well and the windshield cover is less likely to damage other parts of the car. Despite having foil in it foil, it doesn’t conduct, I have tried that in several ways, including puncturing it.
I know people talk about radiant heat from turbo’s and exhausts being a problem. I found the 90-100 deg c air from the radiator to be far more of a problem than the radiant heat from the turbo. How do I know? Radiant would only heat the side that faces the turbo. I found the battery to be evenly hot all over – hot air.
| Airflow from front of car to behind headlight to cool batteries. Previously hot air would come back through through this hole from the radiator. Poor design. |
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| 1.5mm Aluminium sheet folded and edged with rubber seal. |  |
| Blocks airflow from fan onto battery. |  |
| Battery sits on some “windscreen sunshield” as a “floor” for the box. |  |
| Plastic hose to protect sharp edges. |  |
| Cheaper rushed version before trip. Seems to work just as well. |  |
| 100Mile/Hr tape and $2 sunshield. |  |
| Wrapped all around the back, top, sides and underneath. |  |
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| Airflow gaps at the front to allow cool air in. |  |
| Engine close to radiator forces air to go sideways onto batteries. Fan has a large centrifugal component, so a lot of very hot air exits sideways. |  |
Wow Paul – I wouldn’t call FullRiver a cheap chinese battery… there are plenty of AGM’s cheaper than Full River…. and I wouldn’t call their quality cheap either, again – I have seen many other brands that are not as good in terms of quality – not that I have much experience – I only have them in my boat, 4wd, 2 x cars, jetski and two running fridges every week end and another couple I use for other things like running portable pumps and sold hundreds of them which are running in boats and 4WD’s.
Lots of people assiciate “chinese products” with lower quality… not all chinese manufactured product is lower quality than product manufactured elsewhere – I guarantee you – your name brand IT Hardware if it is relatively new is made in one of 3 factories in China. People used to bag Japanese product – now everyone wants Japanese product.
Why don’t you review the expensive AGM’s that are twice the price and see if they are offering real value or is it marketing hype?
Everyone’s entitled to an opinion though… including me 🙂
You have linked the Fullriver HGL series as “cheap Chinese ones” which is both unfair and untrue. We don’t recommend this range for either deep-cycle usage nor under bonnet. I would argue that cheap does not necessarily mean bad either. For deep-cycle applications, use the dedicated DC series with the optional heatshield sheetmetal shroud now available too.
Dave Petrie (Fullriver Product Manager, Australia & NZ)
Hey Dave, get off the soapbox!!! This is his personal opinion, so too bad that you find it unfair and untrue. My experience with the Fullriver series makes me think that they are “cheap Chinese ones” as well. Are you saying that there has NEVER been a problem with one?
Can’t keep everyone happy.
Just wanted to say thanks for the idea. I used some windscreen sunsheild to wrap my batteries and it seems to work great.
Cheers,
Eddie