Battery: AGM vs. Flooded Cell

Look back to 2004 on this forum BFL13

Do you not see my advice about 5% antimony batteries needing 14.7 - 14.8 volts to charge.

That would be SIXTEEN YEARS rock solid inflexibility.

As far as speed is concerned the BRAND of the battery remains fully in the picture. I trust Lifeline to not LIE about their specs. For flooded I trust Rolls & Surrette to not LIE about their data. I do trust Trojan's advice regarding their industrial batteries.

To rely on ADVICE of someone whose opinion rests on incompetent information from some battery manufacturer's SALES AND ADVERTISING dept yields results appropriate derived by its components

" The reason they were going to be used was their higher charge rate. It wasn't 5 times but it was closer to 2 times faster. "

I am hung up on what exactly it means to say "2 times faster"

If that means you can do a 50-90 in one hour instead of two hours, restoring the same number of AH, then how can you do that?

Using a higher charge rate is given as the way to do it. Up to a point you do get a faster re-charge by using more amps per AH size of battery bank. You do not halve the time by doubling the amps, as seen in my ugly graph. It is a diminishing returns thing. But you can do it faster up to a point as seen. (ugly graph shown below)

Also, except for Lifelines, many AGMs specify a high limit on charging rate such as my Starks which say 27 amps per 100AH. So that is no higher than what a Wet can take.

So using a higher charging rate than what a Wet can take only applies to Lifeline AGMs. And I have not seen where they are excempt from the way that higher charging rates means Bulk ends at a lower SOC. So if you did use a way high charging rate, most of the recharge would be in Absorption tapering amps AFAIK.

So you are not going to get twice as long in Bulk at the max amps of the charger to achieve your 2 times faster.

I would like to see, using a charging profile for each case, how the 2 times faster would happen, to compare with the graphs in my ugly graph set. BTW that set is about what I see charging my AGMs and Wets, roughly the same.

Exclusivity

# 1 sin by engineers in the battery industry.

Give the impression that OUR BATTERY IS IN ANY WAY SIMILAR TO SOMEONE ELSE'S BATTERY.

Instant pink slip

Only the BCI prevents companies from adopting 12 hour, 23 hour, or 25-1/4 hour rates.

When Trojan gathered a shipping dock full of warranty RV deep cycle batteries (NOT industrial batteries) THE **** HIT THE FAN. For a decade their absorbsion finish voltage was absurdly low.

However issuing a corrected voltage value the same as anyone else would have preceeded a mass firing of engineers.

Lifeline COULD CARE LESS what "others do".

Most other companies are like a fart in a whirlwind. It's a continuing STP. THE RACER'S EDGE. Hoopla.

Trojan and their INDUSTRIAL BATTERIES are in a different universe.

Wotta Hoot

BFL13 wrote:
You can't charge any faster than your charger's max amps.

There is a slight time saving once you get to the Absorption Stage where the AGM has a little more acceptance rate per SOC, but Bulk Stage timing is about the same.

Some figures from past examples on this topic, noting the %SOC when Bulk ends using various charging rates. (The lower the charging rate, the higher the %SOC when Bulk ends after a time at constant max charger amps)

Wets- 32% and 65%SOC
AGM- 40% and 63%SOC

Wets-19% and 72.5%SOC
AGM- 15% and 75% SOC

So if you are off-grid doing 50-80s you are going to shut off the gen not long after Absorption starts anyway, and you will not realize much of any theoretical time saving by having AGMs.

Solar usually has a very low charging rate, so a high SOC when amps start to taper. This is true with Wets and AGMs. Hard to say if you are any more likely to get to 100% before dark with either type.

Li batts do shine in this regard. At 100% charging rate, they reach 65% SOC when Bulk ends, and at a less stressful (and recommended rate with Battle Borns) 50% charging rate, Bulk ends nearer 80% SOC. Solar with Li means you won't see much of that faster charge with them either due to the low charging rate, unless you have a very large solar array.

We were looking at all this a while back when discussing the wild claim seen in advertising, that AGMs charged "five times faster" :)

Your numbers sure don't match my experience. I used to work for GM on the EV1 back in the day. AGM, although never made it into the car for the public, were experimented with and were going to be the next battery after the FLAs that were used. The reason they were going to be used was their higher charge rate. It wasn't 5 times but it was closer to 2 times faster. I have seen the tests the guy did on the marine how to site. He used old batteries that he even admitted were likely sulfated.

As far as lithium are concerned, My 2 100A lithiums are pretty much in bulk charge with a lithium specific charger until they are 98% SOC. My charger is 60A. The absorption phase is very short and you can see the charge rate taper down to 0 within a few minutes.

theoldwizard1 wrote:

...
Trojan recommends 2.47V/cell on flooded batteries ans 2.45V/cell on their AGM batteries.
...

To restate using 12V; that is FLA 14.82V and AGM 14.7V.

Now, Trojan does not require, they only recommend. Do they specify any minimum charge Voltage, or maybe a range that includes 14.4V. IOW, won't their batteries be just fine at 14.4V?

Over the past five years or so, I have become very picky about matching the charging specs of my charging sources and batteries. My newest inverter/charge on the 620Ah AGM bank has nine charging profiles. I change the profile settings based on average battery temperatures. My solar charger keeps a log of the temps.

When recommending any major change of batteries, don't you agree that it would be fair to consider discussion of the compatible charging solution?

HTH;
John

Deka flooded Vabs is 14.4-14.7v also higher than their AGM Vabs

https://www.eastpennmanufacturing.com/wp-content/uploads/Renewable-Energy-Charging-Parameters-1913.pdf

However, that 14.4-14.7 is lower than for these Stark AGMs at 14.6-14.8 ( my 100AH Starks say 14.5-14.9 same as those UB121000s)

http://www.wegosolar.com/products.php?product=SKR%252d125AGM-Stark-AGM-12V-Solar-Battery-Sealed-125A

Which only proves again that there is no rule that all AGMs use lower voltages than flooded. BUT it does show again that you really need to look up the charging specs for whatever battery you have.

If your charger has AGM, GEL, and WET settings where the AGM voltage is lower than the WET voltage, and your AGM spec is actually higher like the above examples, then you would know to use the WET setting with your AGMs. (If that WET setting matches)

Best thing is to have an adjustable voltage charger so you can meet any spec any battery you buy might have.

I can'tbelieve anyone would spend a dime more for AGMs.
If you use a PD charger there is almost zero maintence on LA 6'ers. A touch of water, and clean the terminals every 2 years, That's it.

BFL13 wrote:
So for these AGMs the charging voltage is the same as for Trojan 6s and for some other 6s too.

Trojan recommends 2.47V/cell on flooded batteries ans 2.45V/cell on their AGM batteries.

BFL13 wrote:
EDIT--here is an interesting review of that above battery, comparing it with some others for deep cycle usage.

https://www.deepcyclemarinebattery.com/reviews/upg-ub121000-deep-cycle-agm-battery.html

Trojan does make a 12V deep cycle AGM, the T1275-AGM. It is rated at 140 Ah vs 100 Ah UB121000. Also 81 lb vs 63 lbs. More lead, more weight, more better !

full_mosey wrote:

theoldwizard1 wrote:
Make sure your battery charging system(s) can handle AGMs. Slightly different charging voltages compared to flooded lead acid.

I wish that people that recommend twin 6V Golf Cart batteries would also caution that the buyer should make sure their charging system will be compatible.

AGMs do just fine with 14.4V chargers. Isn't it common for GC batteries to require 14.8V? And what about the GC equalization charge that can need over 15V?

Never heard of any special requirement for charging voltage of two flooded 6V batteries vs one flooded 12V battery. *

Every good battery charger has a special setting/switch for AGM.

(* The exception to my statement on flooded battery charging are Trojan batteries. For flood batteries, regardless if they are 6V or 12V, their recommended charging voltage per cell is slightly higher (2.47V/cell) than other manufacturers.)

IF you can access the batteries for topping off.. The major difference is COST. I hear lots of stuff about why AGM is better but other than maintenance I have not been able to confirm any of the grand claims.. And I gave them a try. Went back to wet cells.