Anyone want to talk me out of putting an AGM battery under bonnet in GU Patrol

Sorry, should have also mentioned that from all the articles i've read from the forum (via searching) I should be ok, in most cases that i've read. I just wanted to see if anyone had any updated information.

Chri.

My experience is with a GU IV 4.2TDI.

I have a 105 ah AGM aux battery sitting on an ARB tray. It has been there for 3 years, traveled many rough ks and still works fine (touch wood). There has been a lot published about the detrimental affect of under bonnet heat on AGMs, but I have no alternative but to mount there.

The battery is connected to the main via a "smart" solenoid and seems to have no problems charging. I run my fridge, inverter, HF radio, UHF radio and power to the camper trailer batteries from the aux battery.

Maintenance is at least once per month putting the Ctek 7000 on the main battery to charge both it and the Aux battery. Also, the day before each trip I connect up the Ctek to make sure all batteries are fully charged prior to set off (also run the fridge from the day before to make sure all is nice and cold prior to set off).

The bloke at the battery place i get my batteries said dont put agms in the engine bay , they dont like the heat . Why they dont like heat , i dunno . I put 2 exide extremes in the engine bay and 2 ritar agms in the back .

I have an AGM battery mounted under the bonnet of my cruiser for just over 5 years now. OK It's at the front just behind the headlights but it has been happy being there so far.

I have an AGM under the bonnet of my Range Rover Classic. The first battery (absorbed Power) 90AH was replaced after 6 years as it had lost capacity but was servicable.
Regards Philip A

Chris,

everything chemical decays with temperature, batteries included.
This is without use/abuse, so anything like that shortens the life even more.

I've derived a formula if you're interested in the maths:

In order to find out the relationship between life expectancy and battery temperature, you can use this simplified formula:

x=y*(1-((z/168)*(1-0.55^a)))

x...life expectancy in years
y...design life in years which is based on 25°C
z...average number of hours driven per week
a...exponent (increases by 1 for every 10°C step, i.e. under bonnet temperatures: 25°C a=0; 35°C a=1; 45°C a=2; 55°C a=3; and so on)

I've based the formula above on the Arrhenius factor of 45% for every 10°C temperature increase.

e.g:

y = 8 years
z = 30 hours
a = 3


If your under bonnet temperature is 55°C, then you can plug your 30 weekly-hours-behind-the-wheel into the formula,
and the result is: x = 8*(1-((30/168)*(1-0.55^3))) = 6.8 years

If the battery isn't going to last this long, then it's because the charging voltages aren't adjusted according to the battery temperature, and/or the charging current exceeds the max specified value.


cheers, Peter

I had a 120AH Fullriver AGM under the bonnet of my TD 100 series. It died after a couple of years. Hard to say that it was the conditions - the battery didn't show any bulging - but I personally won't be putting another AGM under the bonnet.

I put eight Full River 100 A/H AGM batteries into my boat three years ago. One for starting each engine and six for house use. They were all identical deep cycle units with quite good cold cranking amps and performed both duties well. They had a lot of work to do, were accidentally run dead flat on three or four occasions and still performed well. Heat was not an issue in this case, but they certainly got a pounding.
I would definitely buy Deep River again.

Over the past 12 years I have had a number of deep cycle batteries including an Optima which cost ($480).

The Optima lasted a yr before a cell enlarged and the whole beast was kaput.

The others lasted roughly two years and then started to decline.

Every time I enquired why was this so - the answer was always ENGINE BAY HEAT.

So I removed the Aux battery from the engine bay and relocated it to a 'cold' spot much further back towards the rear of the vehicle.

Da-Da! no further problems


DD

HI had 2 yellow top Optima one starting the other for second battery in my GQ for about 2.5 years both over the front wheels, removed them when I got my GU have now been in there for 3.5 years. They are probably on their last legs and I will probably have to replace them this year. The Patrols both were used only about 5 or 6 times a year so the batteries were on a pulse charger for up to 6 week or more this may lead to longer life span. Well that’s my experience with AGM batteries but in closing I have just put a 130amp AGM under the bed in my Penguin to run the 12v fridge, lights ECT so far so good. John c

Chris I have an AGM fitted in my GU such as you describe and it went in at Weipa five years ago and has done many ks since and is still doing all things like running a 110 Waeco with no probs. Many say they don't like heat but just as many say it does not bother them. I guess that personal experience is the best guide.
Regards.
Ray W.

Hi Chris,

Have you considered a Gel battery?

Cheers Wilko

It depends totally on the Alternator Regulator - if it reduces voltage as temperature increases to match your batteries charge requirements, your AGM will survive - if not, it's expensive.