How long does an AGM Battery Last?

Being a Lifeline I would count on replacing it no sooner than 2019.. Lifeline is the cadillac of AGM's. and usually last around 10 years. I'm assuming the Prior Owner quickly did the upgrade.. That battery is slightly larger than a pair of GC-2's in series just so you know.

I often get into "Which is better threads 2 12s or 2 sixes)

Well, if you had two 8 D's that is clearly better than 2 GC-2, in fact the one you have is better than two GC-2s all by itself.

Other AGM's.. I'd expect to fail sooner, Some within the next year or two. AGM's for the most part do NOT outlast flooded wet cell no matter what my opposition says (I did the test myself).. Lifeline, however I did not test.

I have had way too many small AGM (SLA) batteries fail in a short time. And every one was charged (float) all year.
A 24v B&D mower, the original 12v pair (24v) lasted 8 yrs, used hard ! I was really impressed
A replacement pair didn't go 2 yrs, and one of those was replaced free at 2 months. They were replaced w/ larger lead acid elect chair batteries, (80 bucks each) Going strong at 3 yrs.

Another in a cordless musical amp failed the first month, 2nd going strong at 3 yrs

A week ago, another failed at 2 yrs in my snapper riding mower, $50 bucks for a little bit of a thing !!@#$%^&*

I could only hope the larger RV AGM batts have a better failure rate. But as long as LA RV batts go 8 yrs, I'll stick w/ what works !

I have 12 years old Lifeline AGMs in my RV and they are still at 90% of their original capacity. I've checked them several times with an amp-hr meter. We used the RV about 100 days a year but don't boondocks a lot.

Hi mena,

Except for Mex's two volt cells your L-16 are pretty special.

Bought mine in '09 and they are still holding a charge just as well as when I bought them.

Take a close look at your Lifeline's. There will be a date stamped into the top edge. My last set of Lifeline 8D AGM's lasted for 10 years but the last 2 were clearly showing signs of aging (less capacity). I replaced my Lifelines with Universal Battery AGM's for 1/2 the price and I am pretty happy.
AGM's are substantially better than any other battery option and as long as you do not discharge them below 12V (12.2 is even better) they should last you a very long time.

It's like asking how long does a car last.

Depends on how you (and the previous owner) treat it. In terms of use and maintenance, the only difference of AGM is that they don't need watering and can be left in storage for longer time than regular flooded batts.

Everything else is the same - longer life with proper charging, shorter life with improper charging. Longer life with fewer and shallower cycles, shorter life - with more and deeper cycles.