NOS Sanyo 2500...mystery

For those not familiar with the term, NOS refers to "New Old Stock". (Typically, equipment that requires routine replacement of perishable parts (exampleld tube based amplifiers) that are no longer manufactured will seek out NOS parts at a premium.)

Back in the day, say about 2001, when only Rayovac NiMh were available at reasonable prices (4 for $16 ), my wife secretly bought a blister pack of 8 Sanyo batteries ( 6AA and 2AAA) and stored them away. These were some of the largest capacity batteries of there time and larger was viewed as better.

Some 8 years later as we were re-organizing a closet, they came out. Back then, I did not know much about batteries and this forum had yet to be born. Flash forward to last week.

I pull out the batteries and my worst fears were confirmed. The all measured 0 Volts. I assumed they were toast, probably would not terminate, and probably would have high internal resistance. I put the 2 AAA batteries on the fast charger (0.6C), not hoping for much, and they terminated on the smart charger ....probably sooner than they should have but this was characteristic only of my vibrant batteries. Encouraged, I seperated the AA batteries into 3 sets and put them on 3 different chargers:

1. Smart 2 hours charger (Camelion BC-905a)
2. Smart 280mA charger (Duracell CEF20)
3. Semi smart 250mA charger that trickles above 1.41V

Results:
1. 2 hour smart charger:2. 280mA smart charger:3. 250mA semi-dumb charger:The most amazing thing is that the batteries that terminated on the overtemp of the 2 hour smart charger(see above) were transferred to the CEF20 and terminated but were barely warm (???).

Questions/Observations:

1. Do new batteries tolerated a fully discharge condition (i.e. 0V) better due to some sort of trick introduced during manufacture. This is far below the 0.9V magic number that is recommended that we never discharge batteries below. In this case the low voltage storage condition is due to self-discharge.
2. The negative delta-V termination seems to indicate that 4 of the six batteries are vibrant.
3. The Duracell CEF20 seems to have introduced another "smart" termination condition that does not depend upon a strong negative delta-V signal.

Do packages of NiMh batteries have a best before date or is there some secret preservative that Sanyo is using so that they can be put in a time capsule to be revived years later ?

The title indicates Sanyo batteries but text indicates Rayovac, which ones are you talking about?

The big question is: what is the capacity of the cells?

I had a 2 year old Hybrid discharge down to 0.32v and it's already losing capacity.

The question to me is "Will it hold it's charge". I had some cells discharged to almost 0V, and after a break in they read about 1400mAh or thereabouts... however, 1 week later they're already reading a pitiful 1.2V open circuit and I suspect the discharge may reveal very little capacity retained.

Something similar happened to me almost a year ago. Found a couple of cells that were about 10 year old and when I put them in my LD20 the light lit for a second or so. After a break-in they had even more capacity than stated.

Pretty amazing... but they were nicads and, as they are tougher than NiMH, I think this can be not an exception. They hold pretty well the charge too !

Black Rose said:

The title indicates Sanyo batteries but text indicates Rayovac, which ones are you talking about?

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Apparently PeAK is reffering to Sanyo cells. I don't think Sanyo 2500's were around in 2001 though. As I remember, they came out around 2005.

Interesting results from your charging PeAK. My experience with cells that have sat around, never having been charged like those, are some green "Made In Singapore" 1200mAh NiMH cells that I bought in 2000, or 2001.

I bought 40 or 50 of them for use in rebuilding battery packs, as they were flat tops. Some sat around until about a year or so ago, at which point, some of them had zero voltage.

After two "break ins" on Maha C9000's, 4 out of 5 cells (I still had about 30) were useable and had capacities of around 800-900 mAh. I have no idea what the original "real" capacity was, but these cells seem to hold their charge well, and can maintain 1.2 Volts at a 1C discharge rate.

I suspect that there are a couple of factors at work here. One, they are "1200mAh" cells, and as such are probably a sturdier build than higher cap cells, and two, there may be an advantage to the cells never having been charged. I remember the NiCd dealer I used to buy my NiCd cells from in the 80's told me once, that if you don't charge a NiCd cell, the shelf life will be a lot longer than once the cell has been charged. Use them, or loose them. Maybe this is also true of NiMH cells. It seems to be, to some extent anyway.

Dave

45/70 said:

Apparently PeAK is reffering to Sanyo cells. I don't think Sanyo 2500's were around in 2001 though. As I remember, they came out around 2005.

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Yes...I've edited the original post to make this clearer

45/70 said:

Interesting results from your charging PeAK. My experience with cells that have sat around, never having been charged like those, are some green "Made In Singapore" 1200mAh NiMH cells that I bought in 2000, or 2001.

I bought 40 or 50 of them for use in rebuilding battery packs, as they were flat tops. Some sat around until about a year or so ago, at which point, some of them had zero voltage.

After two "break ins" on Maha C9000's, 4 out of 5 cells (I still had about 30) were useable and had capacities of around 800-900 mAh. I have no idea what the original "real" capacity was, but these cells seem to hold their charge well, and can maintain 1.2 Volts at a 1C discharge rate.

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Your experience seems similar to mine but with older cells. Time has been flying by and my dates with the Sanyo are probably not the most accurate. So I'll go by your dates. Still, 4 years is enough time to fully discharge batteries to 0 Volts.
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45/70 said:

... I remember the NiCd dealer I used to buy my NiCd cells from in the 80's told me once, that if you don't charge a NiCd cell, the shelf life will be a lot longer than once the cell has been charged. Use them, or loose them. Maybe this is also true of NiMH cells. It seems to be, to some extent anyway.

Dave

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I would say that NiCads can be fully discharge and do fine. NiMh seems do worse but the "use them or lose them" probably best applies to Li-ion...though there have been some new developments making them more appropriate for power tools.

PeAK said:

I would say that NiCads can be fully discharge and do fine. NiMh seems do worse but the "use them or lose them" probably best applies to Li-ion...though there have been some new developments making them more appropriate for power tools.

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Yes, it is well known that individual NiCd cells can be discharged to low levels. The point of what the old timer was telling me however, and what I've experienced, is that if a NiCd, or NiMH cell has never been charged, the shelf life is longer.

Now if you charge either chemistry cell, even just once, that changes things. I've had both NiCd and NiMH cells that I charged up, and then let sit for years. These cells do not seem to recover, although NiCd's do a bit better in this regard. So, IMO, "Use them, or loose them" still applies, but again, only once they have been charged.

Also, as I pointed out, ~20% of the green 1200mAh cells that had sat for 7-8 years, never charged, did not recover acceptably. And, as I said, the cells that did seem to recover, were at 800-900mAh. It's quite possible that these cells were never actually 1200mAh, still, the capacity is a bit low.

Dave

Hello Dave,

I would guess that it would be difficult to purchase a cell that had never been charged. Cells are partially charged prior to packaging for sale.

Tom

SilverFox said:

Hello Dave,
I would guess that it would be difficult to purchase a cell that had never been charged. Cells are partially charged prior to packaging for sale.

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Oh, OK. That isn't exactly what I was getting at. The initial factory charge is not a "full" charge. Perhaps this has something to do with it, as well as this being the first application of charge to a virgin cell.

Dave