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Author Topic: Battery capacity lost after 1 year. Why?  (Read 10063 times)
NQ8Z
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« on: September 22, 2016, 09:42:01 AM »

[Posted on another site's forum without resolution]

    My shack runs on 3 x 35 Ah Absorbent Glass Mat (AGM) batteries, same type (PS12350), same brand (PowerSonic). One of the batteries is 1.5 years old, the other 2 are 1 year old. A year ago I checked their capacities with a constant resistance test and all three met specs. One year later, two of the batteries test at half of their rated capacity, one is at its rated capacity. The batteries have no signs of swelling or damage. The individual voltages of the batteries after floating are the same within 0.02V at 13.5 V.

    The 3 batteries are connected by similar cables to a PowerPole junction block which is connected to a high quality charger (A & A Engineering, 5 amp max) and to the rig. The charger maintains the batteries within the manufacturer's recommended range float voltages, at 13.7 V.

    I understand that maintaining batteries at a float voltage isn't as healthy as having a consistent discharge/charge cycle. But is the result this severe in 1 year? And note that one of the batteries still meets its capacity specs.

    Thanks for your insights and suggestions.
     

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KC2MMI
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« Reply #1 on: September 22, 2016, 10:21:25 AM »

The reputable manufacturers all have technical papers online as to proper charging procedures. And some even discuss the quirks of AGM.

AGM batteries, often wrongly called "gel" because they quietly replaced gels for alarm/exit lighting, have their own requirements. In a constant-float environment (like UPSes) they lose 25% per year even if they aren't used. So after two years, a UPS is at 50% capacity, which is why many business users and utility companies replace the batteries every two years.

Also, they can lost 25% capacity simply from being in a hot (~90F) room, compared to 68F. Ad it up, and it can hurt.

The charging voltage also is temperature dependent, they should be on a temperature-compensated charger, ideally using a temperature probe to the battery or at least the ambient temperature at the battery. No compensation? Then the charging voltage can't be optimized, and the battery suffers again.

What ate your batteries? Dunno. If you check the charging voltage with a CALIBRATED volt meter, you may find it was 0.2-0.4 volts off, if the charger wasn't calibrated. That would damage them. If they were maintained at 80-90% charge, instead of 100% charge? That would also damage them, that's a quirk of AGMs too.

Specs, numbers, environment....Oh, also little gray men come around in the night and steal power for their UFOs. (Kidding! Maybe.)

Odds are Powersonic has some fine print out there, compare it all.

Also, the deeper you cycle a better, the fewer cycles it gets. So you might be better off with a single Group31 deep cycle (12v traction or 2x6v golf cart) battery, nearly 100Ah capacity, and something like a NoCo smart charger which monitors and compensates better than a plain float charger will.

And if you read about "equalizing" batteries, most AGMs will die or explode if you try that. A very few premium brands like Lifeline are built to withstand that, and it does help keep their capacity up, but their prices will amaze you.
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NQ8Z
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« Reply #2 on: September 22, 2016, 01:12:01 PM »


All good points, thanks!

35 Ah was chosen so I can carry it, larger would be a problem.

What's really confounding is that two of the batteries were from the same lot and arrived in same shipment.  Under seemingly identical conditions one is at 50% of capacity and the other at 100%. 

I read and re-read the PowerSonic specs but don't see anything I've violated.  I've tried contacting them by e-mail with no reply, yet.

Would non-AGM batteries possibly be better?  (That is, "Gel" batteries)
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WB6BYU
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« Reply #3 on: September 22, 2016, 03:15:30 PM »

Even identical batteries from the same manufacturer aren't exactly identical.
When you float 3 of them in parallel, one likely will draw more current due to
minor differences in internal resistance, cell chemistry, etc.  (The same happens
when you connect the rig to the 3 batteries in parallel - likely it will draw a
different amount of current from each battery.)

Yes, it would be nice if these differences evened themselves out over time -
for example, the battery hogging most of the current would charge up more,
to the point where it drew less current.  But that doesn't always happen at
float levels.  So the battery that is 0.02V lower than the others may get most
of the charging current.

That's a common problem with charging batteries in parallel.
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W8JX
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« Reply #4 on: September 28, 2016, 05:32:05 PM »

Even identical batteries from the same manufacturer aren't exactly identical.
When you float 3 of them in parallel, one likely will draw more current due to
minor differences in internal resistance, cell chemistry, etc.  (The same happens
when you connect the rig to the 3 batteries in parallel - likely it will draw a
different amount of current from each battery.)

Yes, it would be nice if these differences evened themselves out over time -
for example, the battery hogging most of the current would charge up more,
to the point where it drew less current.  But that doesn't always happen at
float levels.  So the battery that is 0.02V lower than the others may get most
of the charging current.

That's a common problem with charging batteries in parallel.

.02 volt difference is not going to cause a early grave get real. Too high a float voltage can cause battery to loose capacity prematurely. 13.5 is a bit high. Most "better" float chargers float at 13.2 and occasionally shift to a higher rate to determine/verify charge state by voltage/current ratio and if good reverts back to 13.2.  Back in old days I remember larger alternators for semi's had a adjustable "button" with tabs you plugged in different ways to select between 13.2, 13.4, 13.6 and 13.8 charge voltage. Long haul drivers than ran highway often in moderate climates usually set them to 13.2 for max battery life and in winter set it higher.
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Ham since 1969....  Old School 20wpm REAL Extra Class..
AG6JU
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« Reply #5 on: November 19, 2016, 06:46:02 PM »

I saw those PowerSonic 35 AH seal battery dies after 1 or 2 years myself.  They were used for solar back up for remote receiver telemetry station. 

for longevity LiFeSO4 or NiMH batteries may be a betetr choice.  35 AH Lead battery real capacity are 2/3 20 AH, so 20 AH is 2 of D NiMH cell.

I do have better experience with  flood lead battery over AGM for longevity, and flood battery I can add water, over charge it , equalize it.
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KC2MMI
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« Reply #6 on: November 22, 2016, 10:52:44 AM »

True gel cells are generally acknowledged as better than AGM cells now, even by the companies that male both and used to push AGM as better. Problem is, gel cells are also more easily damaged by charging problems, so that might be a wash.

It is possible that your batteries were "old stock" before they were sold to you, and sitting on the shelf for 6-12 months could have hurt them. Or, there could be defect issues. Hard to say, but even the telco's replace AGM backup batteries every two years, because they won't rely on how much capacity is left.

And if you have been deep cycling them, that could be a problem as well. Conventional batteries can't put out may deep cycles, and even deep cycle cells really decay much faster when pulled below a 70% SOC.

I can appreciate "because I can't lift a bigger one". You could get six separate 2.2v "fork lift" cells. True deep cycle and wet lead acid, combine them to make one very robust "12" volt battery. That only sounds unconventional until you realize that's normal in the fork lift business, and those machines are expected to perform flawlessly, continuously, all over the world. If one cell goes bad, they replace one cell. Which is still light enough for one (strong) man to lift and carry.(G)
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VE6FGN
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« Reply #7 on: November 22, 2016, 06:36:42 PM »

Is the battery that's still good located in the middle of the string? Often the batteries at each end will fail sooner than those in the middle as they absorb a higher charge/discharge rate than the remainder of the bank.

Not smart on battery banks other than lead acid, however general accepted rule is that you never draw down more than 30% of capacity in order to lengthen battery life. Occasional draws down to 70 are ok, but NEVER exceed 50% draw or battery life is significantly shortened.

Good luck!
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W8JX
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« Reply #8 on: November 23, 2016, 06:43:48 AM »

Is the battery that's still good located in the middle of the string? Often the batteries at each end will fail sooner than those in the middle as they absorb a higher charge/discharge rate than the remainder of the bank.

What theory do you base this on? Even a car battery has a series of cells in one case and none is more prone to fail than others. They all carry same current.
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Ham since 1969....  Old School 20wpm REAL Extra Class..
WA1MOW
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Posts: 19




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« Reply #9 on: November 23, 2016, 03:05:42 PM »

When charging batteries in connected in parallel, you should connect the charger at opposite ends. For example....If the have 3 batteries in a row, connect the positive to the positive post on the left battery, and the negative to the negative post on the right battery. So the all batteries receive an equal charge. If you connect the charger to one battery that battery is always going to get a better charge than the others. The battery at the other end will not get the same charge, if you connect the charger to one end.
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W8JX
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« Reply #10 on: November 23, 2016, 04:20:55 PM »

When charging batteries in connected in parallel, you should connect the charger at opposite ends. For example....If the have 3 batteries in a row, connect the positive to the positive post on the left battery, and the negative to the negative post on the right battery. So the all batteries receive an equal charge. If you connect the charger to one battery that battery is always going to get a better charge than the others. The battery at the other end will not get the same charge, if you connect the charger to one end.

This is good advise but you should also discharge them the same way.
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Ham since 1969....  Old School 20wpm REAL Extra Class..
WA8ZTZ
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Posts: 248




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« Reply #11 on: November 25, 2016, 01:49:24 AM »

When charging batteries in connected in parallel, you should connect the charger at opposite ends. For example....If the have 3 batteries in a row, connect the positive to the positive post on the left battery, and the negative to the negative post on the right battery. So the all batteries receive an equal charge. If you connect the charger to one battery that battery is always going to get a better charge than the others. The battery at the other end will not get the same charge, if you connect the charger to one end.

bingo...    this is the method of connection you will find in trucks with dual batteries 
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G4AON
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« Reply #12 on: November 29, 2016, 08:00:22 AM »

I've operated "hill top" portable for several years. I use lead acid batteries and have tried the cheap flooded leisure batteries sold in the U.K. by caravan shops, tried a premium flooded leisure one and finally bit the bullet and bought a Varta AGM. The flooded leisure batteries were pretty hopeless, one rated at 110 AH measured 33 AH at one year old, a new warranty replacement only measured 60 AH, I gave it away.

The  Varta is now 4 1/2 years old and going strong. I typically don't discharge it below 50% and charge it with a CTEK MSX10 multi stage charger. It is not float charged.

On a previous test with an old flooded leisure battery, charging with the Ctek charger produced greater measured capacity than a simple 2 stage charger did. The difference was 20% as measured on a West Mountain CBA II analyser.

BTW, I don't routinely deep discharge lead acid batteries, not even to measure their capacity.

73 Dave
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KH6AQ
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« Reply #13 on: November 29, 2016, 12:08:02 PM »

The connect-to-opposite corners configuration works for two batteries in parallel. For three or more batteries charge/discharge is optimized by wiring all three batteries to one point using equal cable lengths.
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KD8SKM
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Posts: 9




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« Reply #14 on: November 28, 2017, 10:24:03 AM »

All the above posts is why I use Lithium Iron Phosphate batteries ( LiFePO4 )
5 years and counting and still getting rated capacity with over 1500 charge / discharge cycles.

4 cells in series = 12.8 volts nominal (actually about 13.2 most of the time)

They don't sag when loaded.... nearly flat discharge curve
they don't suffer from out gassing as they are sealed
They return nearly 100% of the energy used to charge (not 65% to 70%)
Charge to 14.4 volts just like SLA / AGM ect.
Half the weight of AGM / SLA
Don't have depth of discharge limitations
I could go on and on...

Cheers,

Rob
KD8SKM
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