AGM batteries seem to be loosing some power. How do I check for bad cells?

nobody928

I bought 4 deep cycle batteries about a year ago made by east penn. I got them used for 50 dollars each.

I have them running in parralel. Yes I know probably not the best idea but it is what it is.

At first the would hold steady around 12.8. but they seem to only stay at full charge verry briefly before dropping down to about 12.4.

Once the drop down to 12.4 they stay pretty stable. What is going on? How can I test or check?

Cariboocoot

Re: AGM batteries seem to be loosing some power. How do I check for bad cells?

"I got them used for $50 each" pretty much explains it.

All you can do is charge them, leave them disconnected for a day, and check the amount the Voltage drops.

Then go buy new batteries.

BB.

Re: AGM batteries seem to be loosing some power. How do I check for bad cells?

Try turning on the loads you expect to run for 1.5 times longer than your desired backup time. If the system runs the required loads forthe required time... You are good to go for now.

'Bill

zoneblue

Re: AGM batteries seem to be loosing some power. How do I check for bad cells?

12.4V isnt worrying per se. In fact it sounds ok. Anything below 24V should get your attention.

It will help if you understand how to use rest voltage to guestimate state of charge. Voltage doesnt really tell you much. However after coming off charge its natural that the voltage drops back, and after several hours of no or little loads, the terminal voltage does fall roughly proportional to remaining capacity.

nobody928 wrote: »

I bought 4 deep cycle batteries about a year ago made by east penn. I got them used for 50 dollars each.

I have them running in parralel. Yes I know probably not the best idea but it is what it is.

At first the would hold steady around 12.8. but they seem to only stay at full charge verry briefly before dropping down to about 12.4.

Once the drop down to 12.4 they stay pretty stable. What is going on? How can I test or check?

Cariboocoot

Re: AGM batteries seem to be loosing some power. How do I check for bad cells?

Am I the only one who read this bit?

nobody928 wrote: »

At first the would hold steady around 12.8. but they seem to only stay at full charge verry briefly before dropping down to about 12.4.

12.8 resting Voltage would be 100%.
12.4 resting Voltage is 75%.
The fact they drop quickly whereas they used to hold steady (presumably under like circumstances) indicates that these cheap, used batteries are near done.

Bill's comment says if they'll do the job, don't worry about it. I would add the OP needs to evaluate the consequences of when they suddenly don't do the job anymore.

westbranch

Re: AGM batteries seem to be loosing some power. How do I check for bad cells?

Not knowing the model of EP AGMs, I am assuming they were headed for the recycle bin, and as such the first charges observed were a surface charge, plus that those AGMs have dried out a bit, possibly from the current charge regimen... the fact that they seem to hold at 12.4 makes me think there is some 'crack -of-the- whip' [(don't remember the exact french spelling) coup de fuet??] effect, so if the loads are not critical,the OP may still get another season, BUT as 'Coot says they need replacement soon...

Distilled, de-ionized water could be added to resurrect them (somewhat) if they are not too far gone but it would all be experimental!

Search for posts by Dapdan and AGMs

BB.

Re: AGM batteries seem to be loosing some power. How do I check for bad cells?

I think Westbranch was looking for:

Low rest voltage on GNB absolyte IIP cells

-Bill

nobody928

Re: AGM batteries seem to be loosing some power. How do I check for bad cells?

I am new to solar and I think that these used batteries have been a great starting point. I have built my solar set up paycheck to paycheck. I have gone through many different panel configuration and charge controllers. I am sure my batteries have suffered a bit from my learning experiences. I am glad that i started with a used "bank" so that I have not in turn broke my "bank account".

I do see your point about used batteries being a bit of a crap shoot but they saved me a ton of money and gave me a good start and some valuable hands on experience. So I would not discredit them.

I live in Arizona and my bank is getting a complete charge everyday. Normally I'm floating by 1pm or so. At the end of the day when the sun goes down, my bank does seem to be around 12.7 however it quickly drops down to 12.4 which seems to happen within an hour. This being said every morning my bank is still above 12.2 or so, it just seems to hover more around the 12.2 to 12.4 range where in the past it seemed to spend more time around 12.7 or 12.6. range

I still feel pretty confident about having another year or so left on these bad boys,I was just wondering if anyone had a similar experience or advice.

westbranch

Re: AGM batteries seem to be loosing some power. How do I check for bad cells?

thanks Bill, that is one of several from Damani...

zoneblue

Re: AGM batteries seem to be loosing some power. How do I check for bad cells?

nobody928 wrote: »

At the end of the day when the sun goes down, my bank does seem to be around 12.7 however it quickly drops down to 12.4 which seems to happen within an hour.

That was my point, (theres always a wise guy , that thats what batterys do when you take them off charge, drop about half a volt.

This being said every morning my bank is still above 12.2 or so, it just seems to hover more around the 12.2 to 12.4 range where in the past it seemed to spend more time around 12.7 or 12.6. range.

The change probably means something. But what kind of load do you put on the bank overnite, how many Wh?

What voltage setpoints are you running. Absorb voltage, absord time, end amps, float voltage?

With FLA you can increase the setpoints somewhat (0.1V/yr) to compensate for age, im not sure id do that with AGM.

jcheil

Re: AGM batteries seem to be loosing some power. How do I check for bad cells?

nobody928 wrote: »

I live in Arizona and my bank is getting a complete charge everyday. Normally I'm floating by 1pm or so.

How do you know that for sure? You can't always judge that simply by the voltage or what the controller says (if it is a cheap controller it's even worse). Too bad you can't check the SG on those. Remember if you have one "bad" battery, it can fool the controller to thinking that the whole bank IS charged when it is really only that single battery that is charged; producing a false reading - exactly what you are experiencing. Then the other batteries sulfate because they are not being charged fully. Especially in your case where you have 4 parallel strings. My guess, just like every other person on here is saying, is that your batteries are shot or at best pretty close to the end of their life.

Go get one of those old-style battery load testers that clamp on to the battery. I bet you are going to find that after a few seconds with a 100-200amp load on them the voltage will drop down to almost nothing (< 10v). That will prove they are shot without a doubt.

niel

Re: AGM batteries seem to be loosing some power. How do I check for bad cells?

drain the batteries as per your normal 12.4v and then shut down the system and disconnect each battery from each other. let settle for about an hour or two and read the voltages of each individual battery. a bad cell will certainly rear its ugly head under these circumstances. if it shows readings with .1v or .2v off from the others as an example then suspect an imbalance in the charging as a bad cell represents in the neighborhood of about 2v or so. an imbalance can swipe some power from being realized and bad wires or connections and especially differing wire lengths or gauges will definitely cause an imbalance.