the lie of rapid NiMH self-discharge

[William Sommerwerck]

I've never had problems with the supposed rapid self-discharge of NiMH
cells. And now I have proof.

Almost two years ago, I visited a friend in Gold Bar WA for Christmas. I
took some camera equipment, including freshly charged NiMH cells for the
flash. I didn't take any flash pictures, so the cells remained unused in the
camera case -- which I just got around to unpacking yesterday. (Really.)

Four of the cells were 2700mAh Sanyo AAs. They all measured about 1.23V,
rather lower than the 1.4V NiMH cells commonly charge up to, but close to
the "nominal" 1.25V of NiMH and nicad cells. Contrary to Urban Legend, they
were not completely discharged.

I put them in a Canon 580EX II, and the flash fully charged up in less than
two seconds. I fired off some shots. The first few recycled "instantly". The
last two took about a half a second. I didn't run down the cells, but it was
obvious that two years of sitting on the shelf had no rendered them
unusable.

The belief that NiMH cells rapidly self-discharge is utter malarkey. Where
it came from, I don't know.

 

[William Sommerwerck]

My phone, my wife's phone, my Dremel nail grinder, and the eight Sony
AAs I bought before I knew about NiMHs, for a starter. These all are
replacements for or successors to products with NiCads, which by
comparison held a charge until needed.

Then why can four NiMH cells sit for two years and still be able to properly
power a high-drain device?

 

[Cydrome Leader]

I've never had problems with the supposed rapid self-discharge of NiMH
cells. And now I have proof.

Almost two years ago, I visited a friend in Gold Bar WA for Christmas. I
took some camera equipment, including freshly charged NiMH cells for the
flash. I didn't take any flash pictures, so the cells remained unused in the
camera case -- which I just got around to unpacking yesterday. (Really.)

Four of the cells were 2700mAh Sanyo AAs. They all measured about 1.23V,
rather lower than the 1.4V NiMH cells commonly charge up to, but close to
the "nominal" 1.25V of NiMH and nicad cells. Contrary to Urban Legend, they
were not completely discharged.

I put them in a Canon 580EX II, and the flash fully charged up in less than
two seconds. I fired off some shots. The first few recycled "instantly". The
last two took about a half a second. I didn't run down the cells, but it was
obvious that two years of sitting on the shelf had no rendered them
unusable.

The belief that NiMH cells rapidly self-discharge is utter malarkey. Where
it came from, I don't know.

so you got dead battery performance and maybe 3 flashes and therefor
batteries don't self discharge?

 

[William Sommerwerck]

So you got dead battery performance and maybe 3 flashes and therefore
batteries don't self discharge?

Where did I say ANY SUCH THING?

I'm going to jump down your throat on this one, because I find most people
don't understand plain English. If I say "Some people have trouble getting
along with their bosses", most readers interpret that as "All people have
trouble getting along with their bosses." Really.

The cells WERE NOT DEAD. After two years they were at the nominal voltage
for a nicad or NiMH cell. Furthermore, they operated the flash without any
difficulty.

 

[William Sommerwerck]

You seem to be drawing a sweeping conclusion based on one data point.
Not always a reliable approach?

It's not the only data point. I've never seen any NiMH cell "rapidly"
self-discharge. At least, not over a period of a month or two, which is the
general claim.

Furthermore, the claim is that ALL NiMH cells "rapidly" self-discharge. I've
seen both MAHA and (now) Sanyo cells hold their charge.

Likely possibility: the NiMH cells that you installed two years ago
use an internel chemistry which is superior to that used in
early-generation NiMH cells.

Unlikely. These are not low-discharge-rate cells.

Newer ones are much better. The ones advertised as "low self
discharge rate" (e.g Immedions, Eneloops, and the like) have been
available for several years, and I believe that the improved
low-self-discharge technologies have begun appearing in more
"mainstream" NiMH cells which aren't specifically advertised in this
way.

These cells are about three years old. And they're high-capacity -- 2700mAh.
To the best of my knowledgte, low-discharge cells have a lower capacity. I
think.


PS: I will not gainsay anyone's claim to have seen rapid NiMH
self-discharge. It's just that I haven't seen it. And I've been using NiMH
cells for almost five years.

 

[mike]

Where did I say ANY SUCH THING?

I'm going to jump down your throat on this one, because I find most people
don't understand plain English. If I say "Some people have trouble getting
along with their bosses", most readers interpret that as "All people have
trouble getting along with their bosses." Really.

The cells WERE NOT DEAD. After two years they were at the nominal voltage
for a nicad or NiMH cell. Furthermore, they operated the flash without any
difficulty.

Your test was unscientific, undocumented, anecdotal, incomplete.
You are certainly entitled to draw any conclusions you wish
and base your personal decisions on those conclusions.

Your blanket statement about NiMH based on your sample-of-one
anecdote requires extrapolation beyond reason. "Proof" is not
a word I'd have used to describe your result.

I can say that my personal experience differs from yours.
And I get along just fine with my boss. Really!!

 

[Cydrome Leader]

Where did I say ANY SUCH THING?

sorry you got 100 full power flashes before the batteries died.

I'm going to jump down your throat on this one, because I find most people
don't understand plain English. If I say "Some people have trouble getting
along with their bosses", most readers interpret that as "All people have
trouble getting along with their bosses." Really.

people that talk about jumping down throats really need to shut the ****
up and not be talking about how to get along with a boss. Really.

The cells WERE NOT DEAD. After two years they were at the nominal voltage
for a nicad or NiMH cell. Furthermore, they operated the flash without any

There's nothing quite like the no load battery test.

difficulty.

yeah, for 3 flashes until the flash was unable to even recycle anymore.

 

[William Sommerwerck]

"Pre-charged" NiMH cells have a lower self-discharge rate,but they don't
seem to be all that more expennsive than regular NiMH.
they are slightly lower in mAH capacity.(2100mAH vs 2300mAH)

I'd ask the OP how many flashes or shots he got from his stored
NiMH cells before they needed recharge.
seems to me that 1.2V is pretty much "discharged" for NiMH cells.
ISTR that 1.1V is the low limit.

I didn't run down the flash. I will do so tonight or tomorrow.

1.25V is considered the nominal operating voltage of nicad or NiMH cells.
(The point another poster made about the relatively flat discharge was
well-taken.) The "discharged" point is, as it is for cells of most
chemistries, 1.0V.

 

[William Sommerwerck]

yeah, for 3 flashes until the flash was unable to even recycle anymore.

You're determined to deliberately misread what I wrote, aren't you?

 

[Cydrome Leader]

You're determined to deliberately misread what I wrote, aren't you?

Go slam some doors or something, you might be better at that than testing batteries.

 

[mike]

I didn't run down the flash. I will do so tonight or tomorrow.

1.25V is considered the nominal operating voltage of nicad or NiMH cells.
(The point another poster made about the relatively flat discharge was
well-taken.) The "discharged" point is, as it is for cells of most
chemistries, 1.0V.

What was the load current for your voltage measurement?

 

[William Sommerwerck]

Hmmm... I haven't done anything with the batteries I used for this
test since May 29, 2011. They've just been sitting on the shelf. I
recall recharging them after I was done with the test. I'll run the
same 1C discharge test again in a few days and see how much capacity
is left after 7 months. This should be interesting. 1C is a heavy
load, but does yield fast results.

Thanks. That would be interesting.

 

[William Sommerwerck]

NiMH cells do NOT totally discharge themselves. They discharge to
about 50% of capacity (by self-discharge) and then just sit there.

Then what is the problem? A 50% loss of capacity is hardly disastrous.

For example, here are some curves I ran for an Energizer 2300ma-hr
cell:
<http://802.11junk.com/jeffl/NiMH/Energizer-NiMH-2300.jpg>
and for an Duracell 2050ma-hr cell:
<http://802.11junk.com/jeffl/NiMH/Duracelll-NiMH-2050.jpg>
There were brand new cells used to test the assertion that NiMH cells
need to be charge cycled a few times before they reach full capacity.
Basically, that's true.

Note the voltages (under 1C load). For the Energizer, it starts off
at 1.35v and starts to die at about 1.10v. If you put a load on your
Sanyo cells, I'm fairly sure your 1.23v no load voltage will drop to
something around 1.18v. In other words, your Sanyo batteries
self-discharged until they were almost dead, and stopped.

But they weren't "almost dead".

This morning, I did what I should have done before I posted. Over a period
of a half-hour, I fired the Canon 580EX II over 100 times AT FULL POWER. The
recycling time was 3 to 3.5 seconds (not unreasonable for full-power
recycling), and the final cell voltage was about 1.21V (before the cells had
time to recover).

100 full-power flashes is not "almost dead". Had I fired on automatic, at a
moderate aperture, not using full power, I could easily have gotten 200 or
300 flashes. And had I been willing to tolerate a 5-second recycle, I
probably could have gotten another 100 full-power flashes.

I recently had a similar experience to what you found. I have two old
Norelco rotary shavers. I received both with dead batteries and
replaced them with NiMH cells of dubious origin. I only charge them
when needed, except this time, when a dry squall dropped a few trees
through the power lines.
<http://802.11junk.com/jeffl/pics/2011-12-03-Storm/>
When I dug out the shavers, the LCD indicator showed a nearly full
charge (about 80%). However, when I tried to use it, both lasted less
than 60 seconds. My guess(tm) is that I hadn't charged it since last
winter (9 months).
That's fairly close to what you observed. There was sufficient
voltage for the LCD indicator to proclaim a nearly full charge, but
not enough stored energy to do much useful work.

That isn't what I observed this morning. The cells, which had sat for almost
two years since being fully charged, were perfectly usable for 100
full-power flashes. I probably have gotten another 100 flashes, but I didn't
want to take the chance of abusing the flash.

The cells are Sanyo Superlattice Alloy EVO, model HR-3U. They were not
shipped pre-charged, and as far as I can tell, they are not
slow-self-discharge ("eneloop") cells. The Sanyo USA site has no information
about them. However, they are available from Batteries America. (Thomas
Distributing doesn't list them.)

 

[William Sommerwerck]

http://store.batteriesamerica.com/h...chargeableni-mhbatteries-2700mahcapacity.aspx

 

[Phil Allison]

"Jeff Liebermann"

NiMH cells do NOT totally discharge themselves. They discharge to
about 50% of capacity (by self-discharge) and then just sit there.

** I have several sets of AA NiMH cells - all Sanyo brand and rated at 1700
to 2500 mAH.

Self discharge is a REAL problem, but no worse than with NiCds.

In general, charged cells lose 90% of capacity in about 6 to 8 weeks -
taking a full 6 hour charge at 400mA to recover.

In my Canon A430, the uncharged cells will run the back display for a few
minutes, let me take a few shots and maybe one flash before the camera shuts
down.


.... Phil

 

[William Sommerwerck]

100 flashes does seem like an almost fully charged battery.

But it isn't, of course. The voltage was at the nominal 1.25V when I
started, but this is well below the end-of-charge voltage for NiMH cells.

However, with such an intermittent load, it would have been nice if you
had a more controlled and more measurable way to test charge level.
If what you say is true, then you may be correct that there's no
self-discharge for a *NEW* NiMH battery. I'm wondering if it might be
a phenomenon that appears later as the battery is used. I'll run my
little discharge test when I have time and get my computer back home.

It was "scientific" in the sense of mimicking photographic use. 100+
full-power shots in a half hour, three at a time, is fairly extreme use.

Incidentally, several people mentioned that you cannot use the
open-circuit voltage as an indication of state of charge. I agree.

Of course. That's one of the problems with nicad and NiMH cells.

However, the fact that the cells read about 1.25V showed they WERE NOT fully
charged. But despite having sat for two years, they were able to give 100+
full-power shots. The point is that their were perfectly usable without
having to be recharged. This contradicts belief that NiMH cells rapidly
self-discharge. (Rates of 1% or more per day are stated.)

I might disable the flash's auto-shutoff and let the cells run down to 1.0V,
then see whether it can still fire more than once. (I have no desire to keep
popping the flash.)

PS: Sanyo says their current eneloop cells (rated at 1500 charge cycles)
will hold as much of 75% of their charge for 3 years.

 

[William Sommerwerck]

"Jeff Liebermann"

** I have several sets of AA NiMH cells - all Sanyo brand and rated at 1700
to 2500 mAH.

Self discharge is a REAL problem, but no worse than with NiCds.

In general, charged cells lose 90% of capacity in about 6 to 8 weeks -
taking a full 6 hour charge at 400mA to recover.

In my Canon A430, the uncharged cells will run the back display for a few
minutes, let me take a few shots and maybe one flash before the camera shuts
down.

I wonder if the "spectacular" behavior of my 2700mAh Sanyos has anything to
do with their "superlattice alloy" construction. These appear to be the only
Sanyos using this design. (That's life, I guess.)

http://en.wikipedia.org/wiki/Superlattice

Anyone care to explain this article to me?

 

[William Sommerwerck]

There is also this quote from Sanyo:
Storage temperature is of high importance if you measure
self-discharge rate. Higher temperatures substantially
increase self-discharging. It is best to store Eneloops
as cool as possible to keep the charge in the battery.
As a rule-of-thumb, every 10°C increase in storage
temperature is equivalent to doubling the storage time.
Some R/C pilots in Europe put Eneloops in the freezer,
with rather good results.
So, how were your batteries stored?

This is the typical "doubling of chemical reactions with each increase of
10°C" rule.

Right before Christmas 2009, I packed up my camera bag for a visit to Gold
Bar, WA. Two packs of NiMH cells were in the bag. When I came home, I put
the bag on the living room floor, where it has remained for almost two
years. The Pacific Northwest is cooler than the rest of the country. The
cells were exposed to "high" temperatures only intermittently, during the
warmer days of Summer.

Presumably, the non-LSD...

Hmmm... Is there a purple owl on these cells?

...batteries would produce much worse results, making your
miraculous Sanyo HR-3U cells better than Eneloop cells,
which seems rather dubious.

Agreed, but we don't know whether the "superlattice alloy" has magical
powers.

Since the Eneloop batteries tested were
brand new, I don't think it's something related to an aging effect.
That leaves your test as an oddity. Are you sure someone didn't
charge your batteries when nobody was looking?

Well, it was around Christmas... Elves, perhaps? Brownies?

Speaking of which... One of Stan Freberg's less-well-known recordings is
"Yulenet", with Joe Friday trying to convince a doubter named Grudge that
there really is a Santa Claus. When they visit the North Pole, they're
greeted by a brownie from the South Pole (Daws Butler doing a silly
mock-Southern voice) who's helping out while Santa is away. I can imagine
the flap such a joke would cause today...

 

[William Sommerwerck]

Ok, I lied[1]. There is a comparison. See:
<http://www.stefanv.com/electronics/sanyo_eneloop.html#compare>
The graph shows the Eneloop battery to be MUCH better at
self-discharge than the conventional NiMH. After 1 year, the Eneloop
retained about 50% of charge, while the conventional NiMH retained
only 2.6%.

[1] I'm suppose to be doing my end of year billing and bookkeeping. I
hate doing billing and am therefore easily diverted. If I go broke,
it's all your fault for creating an interesting diversion.

Extremely interesting.

I'll contact Sanyo and ask them about the self-discharge of my specific
cells.

 

[josephkk]

This might be of interest:
<http://www.stefanv.com/electronics/sanyo_eneloop.html>
It's an independent test of the Sanyo Eneloop NiMH batteries including
some self-discharge tests. Unfortunately, he doesn't compare the
results with the non-LSD batteries. Scroll down to the "Self
Discharge" section heading and note the self-discharge tables.
50% charge loss after 1 year.

There is also this quote from Sanyo:
Storage temperature is of high importance if you measure
self-discharge rate. Higher temperatures substantially
increase self-discharging. It is best to store Eneloops
as cool as possible to keep the charge in the battery.
As a rule-of-thumb, every 10°C increase in storage
temperature is equivalent to doubling the storage time.
Some R/C pilots in Europe put Eneloops in the freezer,
with rather good results.
So, how were your batteries stored?

Presumably, the non-LSD batteries would produce much worse results,
making your miraculous Sanyo HR-3U cells better than Eneloop cells,
which seems rather dubious. Since the Eneloop batteries tested were
brand new, I don't think it's something related to an aging effect.
That leaves your test as an oddity. Are you sure someone didn't
charge your batteries when nobody was looking?

In for a penny's worth; i add that this might be some freaky low self
discharge cells for the given process, perhaps at some process corner for
the set.

?-)