No more AGM batteries for me

[UncleDave]

Since AGM and flooded batteries are both the same chemistry (lead-acid) why would they not be completely interchangeable?

The AGM batteries can typically tolerate more aggressive current draw, but as far as charging goes, since they are the same chemistry I was under the understanding that a charger (or alternator) built for one will work fine on the other.

By and large it will work fine. An AGM battery fits inside the charging profile of a standard wet cell.

What a standard wet setup wont do is charge an AGM most effectively, but not so poorly as to kill it.
Im on 17 years using the same AGM charged with standard alternator.

Less internal resistance than a wet cell gives the AGM both superior charge and discharge profiles.

You can slam amps back into them at a much higher C rating for much longer before heat buildup becomes detrimental.

 

[Hohn]

My X2 survived a discharge below 4V. I’m sold for life.

 

[Mackelroy]

Since AGM and flooded batteries are both the same chemistry (lead-acid) why would they not be completely interchangeable?

The AGM batteries can typically tolerate more aggressive current draw, but as far as charging goes, since they are the same chemistry I was under the understanding that a charger (or alternator) built for one will work fine on the other.

They are completely compatible, but AGM normally holds a higher standard voltage 13v-13.2volt , and an AGM down it the 12,s is more towards end of life.

 

[dishdude]

Why are you testing a 3 month old battery weekly?

 

[stanlee]

Which "good" agm failed after one discharge?

Well I don’t know if it was “good” lol. It is a battery plus Duracell group 65

 

[stanlee]

Its possible that it froze when discharged. Since the plates and separators are next to each other, I can imagine freezing causing damage easier with an agm.

But, any battery can be ruined if discharged and frozen.

The freezing point temperature becomes much higher when a battery is discharged.

No chance. I’m in Virginia, high 40s at worse. Probably 50s as I didn’t even need a jacket.

 

[stanlee]

So will WM replace it?

That battery is no longer in question. It’s in the car. When I got the AGM battery I researched the need for maintenance charging if the alternator doesn’t provide about 14.4 volts (even though mine is pretty close, well over 14v) so I bought a battery charger that could handle AGM batteries at the time. For kicks used the repair mode on the Walmart battery that failed testing and since it’s been passing with flying colors.

 

[stanlee]

Why are you testing a 3 month old battery weekly?

Because I’ve never had an AGM battery before and it takes literally a minute or two.

 

[JimPghPA]

I have a 24 F Walmart MAXX in my 2016 CR-V. Bought it new with an online Walmart price Roolback of $88.00 + tax, on Sept. 11, 2022 and it still test as having CCA in the high 800' or low 900' depending on tempersture and how many days its been since last driven.

I've been watching for a repeat of that rollback price, but have not seen it again.

I'll probably spend 139.99 + tax for another 24 F Walmart Maxx next September.

For a 725 CCA rated battery thats 3 yesrs & 5 monts old, I can't complain.

Measured 2/27/2026: after vehicle sat unused for 4 days.

 

[UncleDave]

I'd still like to know which AGM the OP bought.

Well I don’t know if it was “good” lol. It is a battery plus Duracell group 65View attachment 326561

Thanks.

Standard East Penn product built under a name license deal.

It's not special, but it shouldn't have failed the way it did.

Good would be one of the few TPPL based AGM's.

 

[stanlee]

I'd still like to know which AGM the OP bought.


Thanks.

Standard East Penn product built under a name license deal.

It's not special, but it shouldn't have failed the way it did.

Good would be one of the few TPPL based AGM's.

I pretty much bought it based on warranty. I am going to take it back and see how it goes.

 

[Danno]

I'm beginning not to be an AGM fan. I work at a Ram dealership. My son at a big Chev dealership. Comparing notes at dinner last night, AGM failures this winter, remarkable on how many. No reason for OEs to use a battery that is at least 2x more expensive. Unless it's for stop/start tech, and or increased rigor of crash test results.

 

[Kira]

^^This post constitutes the beginnings of data we need.
I wonder if the failed AGMs tended to be older.

I bought a battery charger that could handle AGM batteries at the time.

Which battery charger did you buy?

 

[E150GT]

My X2 survived a discharge below 4V. I’m sold for life.

I had an x2 in my Mazda for years. Great battery. The prices have gone crazy on them though. I ended up buying a Walmart agm much cheaper. If it lasts half as long it would be ok. The main reason I like them is I don't really have to worry about my battery terminals like I do a flooded battery

 

[Danno]

^^This post constitutes the beginnings of data we need.
I wonder if the failed AGMs tended to be older.

Mostly new cars, and quite a few in service given by the pile I see waiting for recycling.
New vehicles sitting on lots in the winter not being driven is death to batteries. But never this bad until AGMs came out.
AGMs could be hidden cause of so many reliability concerns seen in so many forums.

 

[RaymondP]

Pertaining to the discussion, I have two batteries on my sailboat. One is supposed to be for house (instruments/auto pilot), the other to start the engine. Couple of things to note...

1. The onboard charging system manual says NOT suitable for AGM batteries.
2. I notice both batteries are identical and labelled "Dual Purpose" (Interstate marine). They are NOT AGM batteries.
3. Batteries are wired in parallel.
4. AGM marine replacement batteries (size 24) are close to $300 each. Almost twice as much as none-AGM, although deep cycle and house are priced differently, with dual purpose more costly.

Batteries are three years old and have been on a solar trickle charger at the marina throughout this long COLD winter, and in previous winters. Last time I checked the charger was showing solid green (all good).

Read mixed negatives on Dual Purpose batteries, but don't know what this means technically vs regular (deep cycle/start) batteries. Are there Dual Purpose AGMs or just regular? Appreciate advise on replacement when the time comes. It is no fun trying to land a sailboat under sail at the marina because your engine won't start.

 

[crashz]

One on my many talents is killer of batteries. I try to keep most of my occasional use batteries on maintainers, but I've had pretty bad issues once a battery got discharged. Both AGM and regular flooded batteries in the same application, once they took a significant discharge, they never really came back to life. Specifically, I had both styles in a 2012 Silverado that was rarely driven, and if not kept on a maintainer it would not crank within a week. No matter what I did (other than keep it on a maintainer) batteries would not last in it.

This could be a coincidence or not, but I have found that when 4-way flashers are used when the engines are not running, it absolutely destroys the battery(s). In threes separate occasions, separate vehicles, and different battery types I have had this happen where the flashers would draw down the battery until it would not re-start the engine. Recharge the batteries and they no longer could crank the engine.

 

[thastinger]

I don't mind a rant.

Run on paragraphs with no actual data are an annoyance.

Don't forget the dangling participles.

 

[S62MPOWER]

Just changed out my AGM, lasted 27 months in desert heat. A little disappointing. The good news is it was a 4 year replacement warranty. So the the new unit has a 21 month replacement warranty, the balance of the original.

 

[thastinger]

No chance. I’m in Virginia, high 40s at worse. Probably 50s as I didn’t even need a jacket.

Jan was historically cold in Virginia. For a 2 week stretch, it never got above freezing.