Please Remind Me--AGMs to Full by Ammeter Action?

Phil, to be clear, did the first set of AGMs have the 14.x charging spec and the linked info from that same company didn't care if you used 13.8 instead--or is it just the new batts that have the 14.x spec and you are going by the advice of the other company for the first set of batts' specs?

Just making sure it is apples to apples. Your actual results might be distorted by that alternator charging they get besides what the converter does.

This C&D Technologies easy-to-read-and-understand technical paper is my "bible" in how to charge VRLA (AGM) batteries. Notice that they mention/imply/show-on-graphs throughout the document that recharging of VRLA batteries using 13.8 volts as just another voltage choice one can make for recharging - based on various conditions, parameters, and available recharge times. I can't seem to find anywhere in the paper where it states the one "must use" 14.X volts for AGM recharging in order to keep your AGM batteries from being slowly ruined. The paper of course makes the point throughout that AGM batteries must often as possible be fully recharged to keep from harming them in the long run. (C&D Technologies manufactured my first set of twin 12V 100 AH AGM RV batteries.)

Here's the easy to read technical paper I'm referring to above: http://www.cdtechno.com/pdf/ref/41_2128_0212.pdf

Here's a list of links to a whole bunch of other excellent C&D Technologies publications dealing with VRLA (AGM) batteries: http://www.cdtechno.com/resource/support_doc.html

Seems clear to me that "cycle service" means running them down some and then recharging again as their normal existence. Float service would be like a stand-by power supply or UPS set-up.

Phil has a good reason not to follow the specs exactly ( equipment) and is getting away with it. I think Phil must be right that the occasional alternator charging at 14.x must be what is saving him.

So his example is not any proof that you could do "cycle service" with his batteries using only 13.8v. That is an unknown, unless Mex knows.

MEXICOWANDERER wrote:
Where did you read AGM batteries must be charged at >14 volts?

David .... I read that everywhere, all the time, in these forums.

Also, on the labels of my AGM batteries is says something like "Recharge at 14.4 volts for Cycle Service".

I have no idea what "Cycle Service" means - if there even is an industry standard definition for it. I'm guessing that it means something like: "To help eliminate uncertainty as to whether or not one has reached a full charge after a discharge one should apply 14.X volts for the recharging voltage."

However, I'm assuming that if one is using an ammeter to determine when full charge is reached, one can use less than 14.X volts for recharging - if one has the time. (... Or if one drives long enough and often enough between camping sites so as to get alternator voltage levels applied to one's RV batteries while also monitoring with an ammeter when driving and camping.)

Another thing that I keep scratching my head over is ... for decades "common and industry knowledge" was that for best lead acid battery life, trickle charging should be used over many hours. Aren't "trickle charge" battery charger voltages usually in the 13.X range?

Where did you read AGM batteries must be charged at >14 volts?

Recharging is a game with all batteries. Depth of discharge and this can be expressed as percentage, versus total time needed to recharge. It is anything but a linear formula. Let's keep this limited to AGM.

Discharge 200 ampere hours from AGM. At 1n initial 10 ampere recharging rate it will take something in the area of 25-29 hours to obtain a charge rejection ratio of .50% amperes at full charge where the voltage of course has risen.

With unlimited time plus a guarantee the battery does not end up undercharged the limiting factor is time to sulfation - usually several days. The fuller the battery is the less likely it is to sulfate. A logarithmic scale in interpretation is neither needed nor desired. Problems arise when a recharge cycle takes, say, one week. The damage aggregates. It is cumulative over time.

But again, repetitive failures to fully recharge the battery is the thing to avoid. Being chemical, it too is a cumulative process, tempered by time spent at less than full recharge.

I must have missed something here. GENERATOR RUN TIME is the bugaboo for AGM. I trade max charging potential for time spent to fully recharge. It would be ideal to charge hard for two hours with a generator, then allow the rest of the day to attain point five percent full charge level via solar voltaic. Just make sure the point five percent happens - every day.

With long-term outage I can run the Frightening Harbor 2-cycle for eight hours on a tank of gas/oil at a very light load. This is why I seek those solar panels so I can play hide and go zap with the afternoon sun. As small as that buzzbox generator is, it still consumes fuel and makes noise for a living.

Here's a could be joke - two thousand amp hours of AGM. One half of one percent is 10-amps. Yeah yeah yeah, save it. The idea was presented. Any mention of lithium hexes your converter. Let's keep things organized - the world needs more orgas... ops I mean organs.

Phil, if they won't take any more amps at a higher voltage then AFAIK (not much!) that means they are truly full.

I don't know what the story is on charging at less than the rated charging spec with AGMs. Seems it is ok in your case--it just takes longer.

With Wets it is different, where you must get them to "gas" and 13.8 won't cut it--needs 14.x for gassing. My "learner set" of Wet batts never got up to proper SG with the 13.8 converter no matter how many days I left it on them. Only saw proper SG when I got a charger that could do 14.x.

My particular AGMs want around 14.8 for charging and around 13.7 to Float, so that is what I do. They also specify max of 27 amps per 100AH, so I also stick to that limit. I have no reason to go outside their specs. If I did have a reason, I would have to deal with that (get different batteries or take my chances with these) but I don't, so no problem. :)

BFL13 wrote:
I turned the voltage down to 13.7 for the night and this morning (at 0.01 amp at 13.7 for the pair) turned it back to 14.8 to see if amps would drop to zero like Phil gets as his idea of Full. (Only he does that with 13.8) So amps were back up to 0.9 again at the higher voltage, but later I noticed 1.0 and then 1.1 so amps were rising slowly. Same voltage.

After "charging" (fixed voltage converter) at 13.7-13.8 volts until the current flowing into my two paralleled AGMs is near zero ... and then starting up the MH engine to hit them with 14.2-14.4 volts for a minute or two ... the current into them does not change - it still reads near zero.

So this means I've not done the "full check" test as BF did, because I only left the higher 14.2-14.4 voltage on them for a minute or two after charging them for hours at only 13.7-13.8 volts while observing the ammeter.

Do all the comments in this discussion thread make it clear to me that I've never been charging my AGM batteries up to full by only using my stock converter (most of the time) and the engine's alternator (part of the time) even though the ammeter indicates that current flow into them drops to near zero after hours on the converter - NO.

I've still never read a definitive technical explanation stating unequivocally that to fully charge a dry (AGM) lead acid battery one MUST charge using voltages in excess of 14 volts. All I've ever read implies only that one can charge FASTER using voltages in excess of 14 volts for AGM batteries.

So far per our camping style and being sure to use AGM batteries with a 13.5-13.8 volt float spec, our charging method has kept me from not having to replace our stock 7345 Parallax converter.

If I'd stayed with liquid acid batteries there are solid electro-chemical reasons - beyond shorter recharge times - for at least some of the time hitting them with higher voltages than what a stock converter outputs.

BFL, but...but...but...you realize of course squeezing every last nickel's worth of performance and life out of your batteries means ...cheating... a battery distributor out of his just due income?

The wackos do not realize that maximization of service life and performance is the greenest thing individuals can do....wait...Oooommmmmm...Kumbayah...don't want to be ostracized.

I tried Mex's trick above to see if they were truly full and it worked. Took more than a few seconds to taper back down so maybe they needed a bit more, no idea. Anyway they are happy now at 13.7 and 00.0 amps holding at that with the charging light mostly on, so they are getting some tiny amount of positive amps in when the charging lamp is lit, but not enough to show on the Tri's amps number. Looks good to me! :)

Thanks again, everyone, for the good info on AGM care.

My Northstar when newer would eventually taper to 0.0 amps at any voltage, Now it is pretty rare that i see it take less than 0.2 amps at 14.7v but it is up in the 700 deep cycle range, many of those well below 50%.

My meanwell to battery wiring is a bit stretchy and stretchier depending on load. Dialing in 13.6v after 0.5% of capacity it reached, well sometimes i dial it a bit too low as I am unwilling to wait for it to turn back on as voltage naturally drops. Hours at 13.5v and then dialing upto 13.6v the amps will raise from 0.0 to 1.5 or so, and upto 14.7 goes back up to 2+ amps.

My Northstar defnintely wants 13.6v float, adjusted for battery temperature if more than 20 degrees away from 77f.

Lifeline's manual states 0.5% of capacity at absorption voltage. I seek this goal every recharge.

This tapering 0.5% or less is taking nearly twice as long as when the battery was new. I imgaine it would have gone cliff diving long ago if I did not adjust accordingly.

The tapering to 0.5% duration can be lessened after a deep discharge and a solid 40+ amps is fed to it until it hits absorption voltage and then is held until 0.5%, but this high amp blast restoring some performance is becoming less effective as cycles accumulate.