AGM batteries - Life Expectancy

The reason I ask is so I know aprox when I should replace them.

I've read some websites that say on standby, AGMs can last up to 48 months (only 4 years) and I've read on some other websites that it can be up to 10 years on standby....

So I'm really confused as to why there is so much difference of opinion..

I don't want to know specifically for my situation, because as you say there are many variables, but I just want a ballpark "industry standard" kind of thing...

When people use AGMs in a standby/backup scenario, how long can they reasonably expect them to last?  Not asking for exact timeframes...but just ball park..... is it 2 years or 10 years kind of thing....

Put it this way, I just spent $3000 on eight AGM batteries.... will I need to chuck them next year and buy new ones?  I know a lot depends on the size of the battery etc... So that's why I mentioned they were 100AH 12v batteries.. (they weight 72lbs each).

For $3k, I got 800AH of batteries.... I am tempted to rethink my strategy and buy one of those huge 5000lbs industrial batteries that cost $4,000 but are supposed to last 30 years.

But if my AGMs today will last that long on standby, I won't bother.

Your battery bank is 800AH based upon the 100hr rate. I would consider it to be about 720AH based upon a 20 hour rate.
The typical life for a deep cycle AGM is 4-7 years, for batteries that are being used. (Is the CT battery a true deep cycle, or a hybrid?) Not using them and maintaining a float charge, could actually bring down the life expectancy towards the lower end. At minimum, I would discharge them 10-15% once or twice a month, to exercise them a bit.
Actually, if they were mine, I would cycle them daily.You could easily take 800-900 watt hours out of them, if you increased your PV. (Just how do you intend to recharge all of these batteries after Armageddon, anyway)

You didn't mention any type of battery box. If you put them in an insulated box, it would help prolong the life. I would also put a battery temp monitor on them.  

Keeping the batts at non extreme temps also would prolong the life of the batts according to some mfgs.  I know that in AZ when my batts are exposed to 115 degree ambient, it is detrimental to them; but no way can I a/c my power house.

A couple of you guys are representing the most abusive use of batteries. You can't buy 8 kw of electricity and stuff it off in the garage for when you need it.

Sally your batteries are new. Desulfate them and they should be fine. If they were 6 year old batteries they might not come back at all or very little but if you desulfate them they should work 100 percent. I let my car battery sulfate pretty badly the last 4 months but few charges on desulfating charger fixed it. One more charge should get me 10 or 15 more percent of it's current 80 percent capacity which was down close to 30 percent at the worst.

You can drain a gel battery down to 20 percent throw it in a closet for 2 years and bring it out and charge it back up and it will be fine most times. Can't do that with AGM or lead acid. But you can overcharge or overvolt a lead acid 10 times and it will still peform very well. But you do that 4 times to a gel and it's going to get hurt a little.

If you want an example of extreme abuse in use. I ran a deep cycle down to 30 to 10 percent regularly over 2 to 4 days and overcharged it nearly every time over a day and it took about 200 of those abuse cycles before it started bubbling the last 20 to 30 percent of it's charge, another 40 or 50 abuse cycles before it started bubbling so much that it was just too dangerous to use.

If you want them to work for thousands of cycles just drain em 10 to 20 percent with a light constant load and top em off over and over with a slow good charger.

Manufacterers can't tell you all the low down on sulfation information because it's crystal formation physics and EVERYTHING affects it from the grain structure of the plates when they are made to temperature and barometric pressures to the way the earths magnetic field runs through it. Every rechargeable battery crystalizes in some way be it wet, gel or paste. The crystalization takes the form of paste clumps, gel thickening, or lead acid battery sediments or small coating patches all over the plates. They are naturally at an imbalance with their environment and these processes are how they attempt to put a stop to that.

If you want to prepare for armaggedon. Buy a generator instead and 2 5 gallon gas cans. Pour the gas into your car and put fresh gas in the cans every 6 months or so. Start the generator up and run it for little bit every couple months.

Put those batteries to work or sell them to someone who will.

Hi,
I also have a similar situation with Agm batteries. i got 2 100Amp-hr connected in parallel to my 12volts system in about 6 month one of the battery swell-up while the other remain normal. Iam confused, come to my aid.

Thanks

I know I'm bringing up a potentially dead thread, but I didn't read any good answers for the original poster.�  If I were in your shoes and already had bought this AGM battery bank, and was really concerned about Armageddon, this is what I would do.

Turn the charging system OFF.�  AGM batteries self discharge VERY slowly (1-3% per month).�  They can also handle quite a bit of discharge with no negative effects, I don't know the optimal discharge level - FIND THIS OUT.�  Then I would let the batteries self discharge down to the optimal level, lets say its 50%, so about 1.5 years OF NO CHARGING and NO USE.�  Then charge the batteries and let drain for 1.5 years and repeat until Armageddon.

I wouldn't be surprised if AGM batteries in ideal conditions and under no use could last 50 years or even more, of course this changes when you start using the batteries.

Personally, I would move the batteries inside during the winter (out of habit of using "older" technology), but AGM batteries apparently do not suffer from cold (not sure how extreme they can handle), so you are probably fine with leaving them in the garage over winter.

Another thing to note - do your research on the best way to charge AGM batteries, if you hold them at a constant voltage without a current limiter you will damage them.

http://www.fridge-and-solar.net/agm.htm - fairly informative.