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Old Dec 15, 2015, 07:05 PM
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A123 Battery Capacity vs Storage Time

About 5 years ago I purchased some 2300 mah A123 batteries from an eBay seller in China. They came with paper sleeves and had marks on the ends that indicated that they had had tabs welded to them at one time. I checked the capacity of these batteries and they tested out at about 2100 mah, some a little more, some a little less.

I built a 6-cell pack with these batteries, but did not have an immediate use for it so I put it away and since then I've cycled it a couple of times per year and I always stored the pack at full charge. I know that this is a bad practice with LiPos, but I understood that it is okay with A123s.

I recently decided to put it into a model and before doing so, I decided to check its capacity again. I got a reading of 1620 mah with my iCharger 1010B+. Looking at the individual cell voltages during discharge told me that cell #6 was running out of charge first and of course, once any cell drops below 2.0 volts, the charger says it's done.

Cell #6 is now delivering almost 500 mah hours less than it used to. I thought that I remembered seeing a spec sheet on these batteries at one time that showed that after 10 years storage, the batteries should still have 90% of their initial capacity.

Can anyone suggest a reason why this battery would lose capacity like this? Will charging and discharging the pack a number of time (especially at high current) help to rejuvenate weak cells?

Thanks in advance.
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Old Dec 15, 2015, 10:34 PM
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I would try cycling that one cell independent of the rest of the pack. You might get lucky and it balance out after that and flatten out with the rest of the pack. Of course it is possible that it is bad, or something caused the resistance of it to be higher than the rest. I have a 2 cell pack that if I cycle the cells individually they look fine, but if I cycle it as a pack they wont balance completely.
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Old Dec 16, 2015, 08:23 AM
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I would also do it more than once. It would probably be good to do it to the rest of the cells also.
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Old Dec 16, 2015, 12:14 PM
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I bought two Lifesourse 3000mAh batteries. In each of them one cell always lost voltage quicker and seemed to have more self discharge. Like anything else there can be lemons.
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Old Dec 16, 2015, 05:35 PM
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I have another A123 pack (homemade) with a similar problem of one weak cell. That cell tested out at 1430 mah, when it was supposed to be 2300 mah. I connected the weak cell to the iCharger and proceeded to run fifteen cycles of a 7 amp discharge followed by a 7 amp charge. After a couple cycles, the capacity had increased to 1600 mah, but it never got higher than that.

These batteries are all from an eBay seller in China, and while they may, indeed, be genuine A123 cells, they may have been rejects that didn't meet specs.
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Old Dec 16, 2015, 06:14 PM
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A lot of those were also "seconds", meaning they were harvested from "remanufactured" devices. ie they werent new cells. There are still several places you can buy genuine A123 cells if you are willing to pay for them.
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Old Dec 16, 2015, 08:20 PM
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Not characteristic of my experience with genuine A123's which usually only come from a reputable vendor like WrongWay RC or NoBS Batteries.

When we first started using A123's, eBay was the place to buy the 36 volt DeWalt battery packs that had the genuine cells. Since that stopped as DeWalt quit using the A123's, buying any battery off eBay or anyone else who's offering "low prices" is suspect.
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Old Dec 17, 2015, 01:05 AM
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Quote:
Originally Posted by Zeeb View Post
Not characteristic of my experience with genuine A123's which usually only come from a reputable vendor like WrongWay RC or NoBS Batteries.

When we first started using A123's, eBay was the place to buy the 36 volt DeWalt battery packs that had the genuine cells. Since that stopped as DeWalt quit using the A123's, buying any battery off eBay or anyone else who's offering "low prices" is suspect.
Same here. No telling what quality those cells directly from China had. Especially when they've got pulled tabs on them.

Do note that the current version of the A123's is type "B", 2500 Mah capacity.


The current USA authorized reseller of A123 cells is here:

http://www.a123batteries.com/product-p/anr26650m1-b.htm

I've purchased over 75 cells from this company, a sampling of them showed that they were all within a percent or two of each other in Amp Hours while tested at 25 Amps.

In fact, just received 16 of them today.
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Old Dec 18, 2015, 09:31 PM
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I just finished testing each individual cell in all of my battery packs that were made up from these A123 cells that I got from China. The test results showed that the cells basically fell into 3 capacity ranges - 1650 mah hours, 1850 mah, and 1950 mah. (These numbers are approximate and vary from battery to battery, but you get the idea). Only one pack had batteries that all came in at 1950 mah, so this pack is usable as it is. The other two packs are a mixture, with each one of them containing a cell that only has 1650 mah capacity. That means that I can't draw more than 1650 mah from the pack, regardless of the capacity of the rest of the cells and that makes these packs unusable as far as I'm concerned. Looks like I'll be using those cells that I just bought from a123batteries.com to make a couple of new packs.

When I got the batteries from eBay, I should have done a capacity check on all of them and I might have seen that they were defective. The other problem was that the A123 data sheet only gave a nominal capacity of 2300 mah, but not a minimum value. Some other users of A123 batteries on this forum stated that A123 cells never delivered their advertised capacity, so I wasn't sure what criteria I should use to judge whether the cells were defective or not. Now it looks like I have about $100 worth of useless batteries unless I can find an application where I only need A123 cells of lower capacity.

Thanks, everyone for all of the information on this thread. Live and learn, I guess.
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Old Dec 18, 2015, 11:45 PM
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Quote:
Originally Posted by Warthog_Fan View Post

Some other users of A123 batteries on this forum stated that A123 cells never delivered their advertised capacity, so I wasn't sure what criteria I should use to judge whether the cells were defective or not.

Thanks, everyone for all of the information on this thread. Live and learn, I guess.
I've also purchased some A123's directly from China. They only lasted 5 years and 500 flights while pulling 40 Amps per cell. Who knows what China is selling now.

At any rate, these cells were purchased from http://www.a123batteries.com/product-p/anr26650m1-b.htm who is a factory authorized supplier. I've purchased well over 50 cells from them so far. And, all of them were very close in their milliampere hour capacity.

The current A123 version is their type "B" cells rated at 2500 Mah. It should be noted that the mfg rates their 2500 Mah while discharging all the way down to two volts per cell. And, they provide 2500 Mah.

Attached is a JPG of tests I ran on the authorized A123 2300 Mah type "A" cells versus the A123 2500 Mah type "B" cells. The test current in both cases is 25 Amps.

I did find out that testing A123 cells with a pressure type contact, rather than a soldered connection will result in significant voltage drop while pulling 25 Amps at the pressure type connection.
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