AGM batteries - are they better?

[DryCamper11]

Upgrade to an AGM battery. You can safely mount them inside, and upside down, and they will out-perform any flooded battery you ever owned!

Here's a quote from another thread. It's typical of others I've seen. I wonder if anyone here can convince me it's correct. Clearly the AGM has some advantages. Two are seen in that quote - inside and upside down. If you need to mount upside down and can't ventilate, sure, that's an advantage, but I don't need those advantages and don't want to pay extra for something I don't need.

We're left with the rapid charge rate they are reputed to permit. I would love to run my 80A charger at 80A continuously until I reach 100% SOC. Right now my 460AH FLA batteries recharge at 80A from 50% SOC for about 3 hours (some fluctuation in current - slow climb from below 80 to above 80 during the first hour as they warm up then down to 70+ at the third hour), then begin to taper more rapidly during the last hour as the battery voltage approaches the charger voltage.

Does anyone have charge curves for AGM showing the performance (preferably with an 80A charger)? I'd particularly like to see the tail end of the charge cycle. How do AGMs perform? Is it significantly better than FLA batteries? Do AGMs taper the charge rate the way FLAs do, or is the entire advantage in the fact that I could run a bigger charger (100+ A) for my 460AH battery bank?

Are there other advantages that AGMs offer?

[Almot]

The thread subject was indeed "which is better", but the OP had clarified what exactly were his criteria of "better" - mostly the rate of charge and tapering close to the float stage.

[beemerphile1]

harold1946 wrote:

I simply used the criteria provided by Deka to illustrate their overall rating.
The subject of the thread is, "which is better" meaning the battery itself, not which one is best in every application. Deka did not address that. Neither did I. :R

No need to be defensive. I did not criticize your post, only pointed out that different assets are important in different uses.

In reference to the thread title, there is no superior battery in every use. In my fleet of vehicles and RVs I use flooded, AGM, and Gel depending on the use.

If anyone wants to talk "better" or superior we should also include nickle and lithium batteries. Why limit the discussion to only lead/acid batteries?

[harold1946]

beemerphile1 wrote:

harold1946 wrote:
Using the figures submitted by Deka and the 19 criteria, with the assesment values provided AGM's come out on top.
Ignoring cost and any specila charging requirements, this is where the evaluation comes out.
wet cell; 49/19=2.157
AGM; 59/19=3.105
Gel cell; 54/19=2.842
Draw your own conclusion.

Keep in mind that you cannot go strictly by that measure. Anyone looking at the list needs to weight the issues important to their particular use.

The chart you are looking at weights everything equally but in the real world some things are more important than others to an individual consumer.

I simply used the criteria provided by Deka to illustrate their overall rating.
The subject of the thread is, "which is better" meaning the battery itself, not which one is best in every application. Deka did not address that. Neither did I. :R

[beemerphile1]

harold1946 wrote:
Using the figures submitted by Deka and the 19 criteria, with the assesment values provided AGM's come out on top.
Ignoring cost and any specila charging requirements, this is where the evaluation comes out.
wet cell; 49/19=2.157
AGM; 59/19=3.105
Gel cell; 54/19=2.842
Draw your own conclusion.

Keep in mind that you cannot go strictly by that measure. Anyone looking at the list needs to weight the issues important to their particular use.

The chart you are looking at weights everything equally but in the real world some things are more important than others to an individual consumer.

[harold1946]

Using the figures submitted by Deka and the 19 criteria, with the assesment values provided AGM's come out on top.
Ignoring cost and any specila charging requirements, this is where the evaluation comes out.
wet cell; 49/19=2.157
AGM; 59/19=3.105
Gel cell; 54/19=2.842
Draw your own conclusion.

[pnichols]

Wayne,

Outstanding observations!

It seems to me that, given what you are saying, AGM batteries hands-down have at least that (tremenduous?) added advantage over FLA's ... which in many cases might mean that an RV'er who switches to them might not need to spend additional $$ to replace their stock single-stage 13.8V converter. Obviously I never replaced mine ... used the saved $$$ for other RV mods.

What you mention probably is related to two things:

1) Some AGM batteries are designed to be floated in the 13.5V-13.8V range.

2) All AGM batteries intrinsically have much lower internal impedance than FLA batteries ... hence AGM batteries, if needing a charge, can also suck up pretty good charge current at only their float voltages.

[Wayne_Dohnal]

- They seem to defy all forum-knowledge by both floating and charging (when camping) from the same fixed voltage ... ~13.8 volts from a stock converter.

I saw this immediately when I put an Interstate AGM battery into the prior RV that used a Magnetek 7345, 13.8 volt converter. When discharged even slightly, the battery would pull pretty high current, then taper off to almost nothing when recharged. It appeared that a multi-stage charger would offer no benefit whatsoever. The specified float voltage for many AGMs is 13.5 to 13.8 at 77* F.

[pnichols]

full_mosey wrote:
We should get a free pass for early failure!

EITHER as you say ... OR (in my case) ... maybe AGM manufacturers consider use in a wheelchair as a mission-critical application requiring ultra-high design and/or construction quality (haha). 😉

[full_mosey]

Hi Phil;

I converted beginning Jan 2009. If those are your first set of AGMs as is my situation, I would consider them a training set. We should get a free pass for early failure!

I bought three of them a year apart, after which I changed from a pop-up to a TT, and added two 12V fridges and solar to the mix with the current set. It is a stretch to call them a set as I grew into them; more an adventure.

HTH;
John

[pnichols]

I admit I'm heavily biased, now, towards AGM batteries for my motorhome MAINLY based on my personal experience with mine instead of what the experts publish:

- I bought 'em in the fall of 2006.

- They still do their thing on camping trips.

- There's never any corrosion around them.

- I never get holes in my pants if I brush up against them.

- They're never thirsty.

- I get to pay no attention to how far I draw them down before recharging.

- They seem to defy all forum-knowledge by both floating and charging (when camping) from the same fixed voltage ... ~13.8 volts from a stock converter.

- They're fully charged from the 130 amp Ford alternator (when driving) during 5-6 hours of travel.

Maybe it's because I screwed up by buying wheelchair AGM batteries instead of buying AGM batteries advertised to be for recreational vehicles. :h

[harold1946]

Although not all are members here, all motorhomes built by CT Coachworks have 2 Deka MK 8A8D 245 AH AGM house batteries as standard equipment.
The last count that I am aware of there were 140 coaches built, so that would be 280 AGM batteries.
Not everyone that has AGM's are members of RV.NET

[mena661]

BFL13 wrote:

Mena, you can't dig your way out. Even your sister the mermaid has AGMs and she is NOT AMUSED by your statements!

LOL! She's so lazy! She can't even bother to smile or maybe that is a smile.

full_mosey wrote:
The battery will be 5yo in Jan when we are going to dry-camp for a month in Q'zite. Should I trust it or get one of those $180 100AH grp 31s? 🙂

It's working, I'd trust it. Although, can't go wrong with more amp-hours.

[full_mosey]

Almot wrote:

1) Recovery after discharge below 50%, AGM is better than FLA. My UPG AGM warns not to discharge below 60%. Maybe Deka AGM is radically different and SOC below 50 doesn't affect it instantly (didn't try to do this to my AGM, though I doubt it will affect it instantly), but AGM being "better"?

2) Shelf life, Starting FLA = AGM. Since when shelf life of any FLA is same good as AGM?

3) Low initial cost, Deep Cycle FLA = AGM. I don't know, maybe this is true for Deka, their FLA are not very common, but this is definitely not true for other brands. AGM technology is getting cheaper so the gap narrows, and bargains can be found if you shop around, but generally, $/AH AGM is more expensive and this makes sense because technology is more complicated.

1. Well some are just resellers of batteries mfgrd elsewhere. Who knows what the specs really are? Deka has their own plant. I do have an 8a24m 79AH and it has survived several morning readings of 11.8V which is pretty close to a resting reading. No telling how low they went overnight. Also, I have dry-camped for 31 consecutive nights by recharging with solar and genny. The battery will be 5yo in Jan when we are going to dry-camp for a month in Q'zite. Should I trust it or get one of those $180 100AH grp 31s? 🙂

2. I'll bet it has something to do with Antimony or Calcium. Notice the deep cycle is = 1, probably same reason.

3. Possibly for non 6V GCs which are higher cost. They do list flooded dual purpose as cheaper than AGM which is right.

HTH;
John

[BFL13]

mena661 wrote:
PN, there's cons just none of the AGM owners want to hear them. When i was researching batteries, I had pros and cons for FLA vs AGM and chose FLA based on that and input from forum members.

Mena, you can't dig your way out. Even your sister the mermaid has AGMs and she is NOT AMUSED by your statements!