Maximum amps for testing AGM capacity?

[Naio]

After a winter of being very sick, and a spring of catching up on farm chores, I am finally back to being able to work on the van at least once in a blue moon. Next step, testing the 100aH Fiamm telecom batteries I got used. I've been topping them off periodically, but otherwise haven't done anything with them since hitting them with the meanwell to recover capacity last year.

My question: How many amps are ok at continuous load, if I want to run them each down to 12 volts for testing? Is 30 ok? 60?

I have the van in storage, so I can't hang out for too many hours during testing. And, since I finally got this giant heavy batteries to the van, I don't really want to move them back to my house :-). But I have killed AGM deep cycle batteries before with too many amps, and certainly don't want to do that.

In case it matters, things I have available for load are a couple of 300 watt heaters, 600 or 900 watt ones, lamps with 60 watt bulbs, and assorted minor loads. I don't have anything 12-volt, so I will be running this off an inverter.

[Naio]

I'm working on the testing. How hot is too hot, for the terminals?

The battery I tried first is it one with a suspected bad cell. After a couple of minutes it got up to 111 degrees, so I quit the test.

But the next battery I did, my suspected best battery, got to 108. It didn't go higher than that, so I did the 10-minute test. I'm using a 40 amp load.

[Naio]

pianotuna wrote:

But for you to check if they are junk--charge as much as you can tomorrow, then the next day put on that 900 watt and 600 watt heater (if the inverter can do it). Look for voltage to go down. Run it for ten minutes. Disconnect the batteries from each other. Wait 20 minutes then check to see if the voltage has recovered. If it has the batteries are ok. Do be sure to recharge before you leave on the second day.

Thank you for the suggestion. I wasn't able to do any testing yesterday, and only have a few hours today. (I'm kind of stressing about this situation.) Your quicker test will be easier for me to do today. I'm wondering how much of a voltage rebound I should be looking for, but I guess I will just post my numbers when I'm done and see what you all think :-).

I have a meanwell that will do up to 30 amps, so I can top off the batteries while I am there too babysit it.

Where is our dear Mex? He doesn't usually miss a battery conversation, and this worries me. I hope I have not missed some horrible news.

[BFL13]

pianotuna wrote:
The PD does a "stir" every 21 hours (14.4 for 15 minutes).

Some other converters do that too, calling it a "fourth stage". There has been some derision on this forum about the possible efficacy of that. I have no measurements or data to say whether it works or not.

I have seen that doing a deep cycle at home before leaving, means you get a longer 50-90 first time out. You do get an extra 10% the first cycle, but even with that, it still goes longer if you do that deep cycle at home before leaving. But I do not have a converter that does the "fourth stage" trick.

[pianotuna]

The PD does a "stir" every 21 hours (14.4 for 15 minutes).

[BFL13]

mike-s wrote:

BFL13 wrote:
If you only have 13.6ish and they do fully charge, what about stratification? How often do you mix the electrolyte, and how if you don't have a higher voltage to do that with?

Just, you know, drive down the road. A couple hours of driving will mix things up as well as an equalization cycle.

Only if there is an election coming, and your friendly politician does not think he must re-pave the roads to get re-elected. Here, the roads are smooth because the politicians are afraid. 🙂

Never mind that once on the road alternator charging at 14.x takes place as well as any bumpy rides.

"Exercising the batteries" is recommended at least every two months when on a long term Float.

[mike-s]

BFL13 wrote:
If you only have 13.6ish and they do fully charge, what about stratification? How often do you mix the electrolyte, and how if you don't have a higher voltage to do that with?

Just, you know, drive down the road. A couple hours of driving will mix things up as well as an equalization cycle.

[pnichols]

FWIW, I don't think that AGM batteries can stratify. I could be wrong on this, but so far I've seen nothing in writing to the contrary.

[BFL13]

If you only have 13.6ish and they do fully charge, what about stratification? How often do you mix the electrolyte, and how if you don't have a higher voltage to do that with? Not a worry with AGMs AFAIK.

[pnichols]

pianotuna wrote:
There are those who would say 13.6 won't ever charge a single battery fully.

That's mostly the voltage I use for my two (expensive) 115 AH Group 31 12V AGM deep cycle RV batteries. The ammeter eventually goes to zero amps being accepted if I leave them on 13.6 volts long enough.

Maybe I'm slowly destroying my batteries - don't know - and so far for years in these forums no one has been able to provide a clear and simple electro-chemical engineering based reason(s) as to why I am slowly destroying them. They get mostly charged during trips and floated month after month after trips using that same 13.6 volts and a permanently installed ammeter for monitoring their continual charging current acceptance rates.

I've read several technical papers on lead acid battery charging and so far none have stated outright, or implied, that 13.6 volts is a slowly destructive way to charge lead acid batteries. The technical papers only state/imply that it will take LONGER to fully charge lead acid batteries using 13.6 volts and that whatever charging voltage is used - the batteries should not sit too long between charges with no charging voltage being applied - which I understand the electro-chemical reaon(s) for.

I've saved around $200 dollars by continuing to use (mostly) the stock converter that came installed in the RV for charging of it's coach batteries.

[pianotuna]

There are those who would say 13.6 won't ever charge a single battery fully.

I used to charge 875 amp bank of flooded cells with a 35 amp PD with wizard. It took a long long time (a week on shore power) but it would eventually get there.

But for you to check if they are junk--charge as much as you can tomorrow, then the next day put on that 900 watt and 600 watt heater (if the inverter can do it). Look for voltage to go down. Run it for ten minutes. Disconnect the batteries from each other. Wait 20 minutes then check to see if the voltage has recovered. If it has the batteries are ok. Do be sure to recharge before you leave on the second day.

Naio wrote:
BFL wrote:


I don't think I can put all four batteries in one bank, because I don't have proper charging capacity. I have an 80 amp PD.

[Naio]

BFL wrote:

You can do a test to see if the batteries are any good at all, but that might be all you want to know.

If you put a load on them and their voltage does not "collapse" but goes down in a regular way, you are good to go.

Yes, as MrWiz implies, I am not up to rigorous, scientifically valid testing right now.

I just want to find out: 1. If any of the batteries are junk, and 2. Which ones have similar charging and discharging characteristics, so that I can connect them in pairs.

I don't think I can put all four batteries in one bank, because I don't have proper charging capacity. I have an 80 amp PD.

I appreciate the comment about watching for voltage that crashes.

Is there anything else people think I should try to learn from my funky testing, that would help me with my build? I'll be able to mess with them for an hour or two today, and a few hours tomorrow, and then I won't have access for a few weeks.

[MrWizard]

she is building a camper van
the batteries (4?), will be split into (2) pairs
the van is in storage
she can go test the batteries
she cannot (right now) spend the weekend doing a simulation

a max load timed test, will give a general idea of amp Hrs available
real time use with intermittent loading, and battery recover time, will provide
more ampHrs than the the test use

[Sam_Spade]

Naio wrote:

I think what I need to know is, how many usable hours can I get out of each battery, and I think going down to 12 volts will tell me that. Am I wrong?

Only in that you are trying to find out what the MAXIMUM drain is that you can apply to do the test.

That is not a practical way to gauge the USABLE number of hours that you can expect in actual use.

If you can't reasonably estimate the draw in actual use, then the "standardized" test rate would be better than slapping a huge load on them.

AND.....if they are all 12 V batteries, you really have no choice in how to interconnect them, in "normal" use. They have to be in parallel.....unless you can somehow split the loads or have a transfer switch.

Sometimes the battery nerds do more harm than good. 🙂

I say one more time: Connect as many of them together as you can and do a "live" test with a simulated camping weekend.

Understand, however, that your charging system (converter/charger) probably is NOT capable of recharging a bank of 4 batteries in a reaonable amount of time. It likely wasn't designed to do that.

[pianotuna]

BFL13,

Low voltage cut out varies by brand. I think it is only 10 volts on my Magnum. Far too low really. It is adjustable from the remote but I've been too lazy to reset it.

On the whole, I miss my flooded jars because there were many more cells, and so less voltage drop. However, I don't miss laying in the snow to top them up.

Firefly 2 volt cells mmmmmmm 🙂 https://www.bruceschwab.com/wp-content/uploads/sites/86/2018/04/Firefly-handout.pdf