AGM Battery Life Expentancy?

Submitted: Tuesday, Mar 25, 2014 at 10:14
ThreadID: 106890 Views:2053 Replies:5 FollowUps:7
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I have an AGM battery as a second battery in my ute which I drive daily. It must be at least 4 years, maybe 5 years old. It's had a pretty easy life, not being used very often (compared to how often the main battery is used).

When it was brand new it read about 13 volts, over the past year it has continually read about 12.6 volts.

What's the life expectancy of AGM batteries?? It's a reputed good brand battery.

Thanks for any help.
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Reply By: HKB Electronics - Tuesday, Mar 25, 2014 at 10:29

Tuesday, Mar 25, 2014 at 10:29
How long is a piece of string?

You partially answered your question, the less you use it and the less deeply discharged
it is then the longer it will last.

If you drive on rough roads a lot of the time, then mechanical damage will also come into it.

6 years is pretty good, you might get 10 but that's probably pushing it, bottom line though if you you were intending to do a 6 month trip to remote areas and relying on the battery to keep your freezer going etc I would replace every 4 years or so. If your only using it now and again around town I would keep it there till it dies.


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Follow Up By: Razerback - Tuesday, Mar 25, 2014 at 10:58

Tuesday, Mar 25, 2014 at 10:58
There are hybrid AGM batteries and then there are deep cycle, often the type of battery is not stated depending on brand as both are suitable for cycling however the true deep cycle versions have thicker plates and are more suitable to discharging and recharging to certain levels. The 13.0 volts vs 12.6 volts also depends on when you measured the battery after charging? You might also want to charge the battery via a smart charger and then measure again. 6 years is around normal I would have thought, up to 10 is not uncommon depending on use and management.
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Reply By: Siringo - Tuesday, Mar 25, 2014 at 12:53

Tuesday, Mar 25, 2014 at 12:53
Thanks for the useful information.

I have never charged the battery as it's wired up via a Redarc isolator and I thought that's all you needed to worry about when it came to recharging the battery???

I drive the car daily, does the second battery need recharging in that case??

Thanks again.
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Follow Up By: HKB Electronics - Tuesday, Mar 25, 2014 at 13:08

Tuesday, Mar 25, 2014 at 13:08

If your car has a standard alternator that's charging at around 14.4V @ 22C ambient then no you shouldn't need to but the occasional charge with a charger won't hurt.

If you have one of the newer models with a low voltage type alternator, ie Toyota diesel Prado or 200 series etc and using a simple VSR then a booster diode will put you write.

If you have one of the ECU controlled models then a DCDC charger would be required but as you indicate it used to charge up to 13V I would suspect none of the above applies.


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Follow Up By: HKB Electronics - Tuesday, Mar 25, 2014 at 13:40

Tuesday, Mar 25, 2014 at 13:40
Make that:

"I would suspect the last two don't apply"

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Follow Up By: Siringo - Tuesday, Mar 25, 2014 at 14:34

Tuesday, Mar 25, 2014 at 14:34
My vehicle is a 2010 D40 Navara. I'll see if I can get any info off the alternator.
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Reply By: The Bantam - Tuesday, Mar 25, 2014 at 20:02

Tuesday, Mar 25, 2014 at 20:02
If it is indeed a good brand that publishes a full spec sheet, there should be some service life graphs, that take into account temperature,and other factors.

A while ago I read a paper written and researched by on aof the caomanies that makes AGM for stationary use.

They proved by actual testing that you could reduce the best reasonable life expectancy of 10 years to less than a month by poor treatment.

Then there is actual measured performance.

Most batteries are replaced when they fail......but truth to tell they have been well below spec for a long time before that.

What do you consider is acceptable performance?

These days I own a couple of testers that will quantify battery performance....most people don't have this luxury. realy is an open question.

If you have got 5 good years out of any battery you are doing well.

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Reply By: Member - Phil G (SA) - Tuesday, Mar 25, 2014 at 23:14

Tuesday, Mar 25, 2014 at 23:14
Your setup - where your alternator is charging the AGM with no restriction on the amps, you may have shortened its life already. Common AGMs such as FullRiver and Remco (and pretty much all others apart from Optima and Lifeline) will have a maximum current on their spec sheets or written on the battery case. For 100Ah battery, this is usually around 25amps. If your alternator is allowed to pour more than 25 amps into the AGM the battery can vent - reducing its capacity eventually to the point where the battery becomes pretty useless. I measured 45 amps going into a brand new Remco after a couple of days camping - because I had good wire and a decent alternator.

If I were you I'd do a battery capacity check. Simple way to do this at home is to firstly fully charge the battery on a multistage charger, then run a fixed load (I use a 13W fluoro that draws 1.1 amps) for a long time while you're monitoring the voltage. See how long it takes for the voltage to drop to 12.0V - should take 30-40 hours for a good battery.

The Remco AGM mentioned above only got a few hours when I did this this test - it was only 2.5 years old, never been mistreated apart from the fact that it was subject to high alternator currents.
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Follow Up By: Siringo - Wednesday, Mar 26, 2014 at 09:36

Wednesday, Mar 26, 2014 at 09:36
That's interesting info, thanks for that. I might start looking at a more intelligent isolator than the basic one I have now.

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Follow Up By: Member - Phil G (SA) - Wednesday, Mar 26, 2014 at 09:56

Wednesday, Mar 26, 2014 at 09:56
A 20A DC-DC charger is the easiest way to limit current to 20A. Here's a spec sheet for a typical AGM. You'll see the initial charging current for this 105Ah battery is 21A or smaller.
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Follow Up By: HKB Electronics - Wednesday, Mar 26, 2014 at 10:30

Wednesday, Mar 26, 2014 at 10:30
Phil G,

An alternator is no different to a DCDC charger, if the battery will accept more than 25A the alternator will supply it, so will a 40A DCDC charger.

As most people rarely drive for more than 4-5 hours a day when touring why would one install a battery capacity that can only take low charging currents? if you have 200Ah of useable capacity and you use it and many do, then your looking at 12 hours drive time to charge the batteries.

Mind you many still do use these batteries and charge them at a higher rate yes it will shorten their life somewhat but that's is a trade off against quicker recharge times.

If you only use them for the occasional weekend away then slow recharge times probably don't matter.

Recharge currents can also be controlled by the us of appropriate dimensioned cable when charging straight off the alternator but most people are trying to reduce charge times not increase them.


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Reply By: Mark T6 - Wednesday, Mar 26, 2014 at 17:47

Wednesday, Mar 26, 2014 at 17:47
I had to replace one prior to doing the CSR last year.....I was so lucky that it collapsed on me in Kalgoorlie so was able to slip in and get a new one on the very morning we departed for Wiluna.

It hadn't missed a beat for 3 years BUT we had done a fair bit of rough road travel, and maybe 120-150 nights of remote camping in that time.

It was just used to run a Waeco 50 litre (as a fridge / freezer) and some LED lights, nothing else.

Started to lose power on the few days we were in Kalgoorlie, and that was even after doing a bit of running around in the Prado (well and truly enough running around to charge it up).

Ten years sounds incredible, even six would be great....mine lasted three!!
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