Re: Unused Li-ion battery pack

On Thu, 01 Oct 2009 20:22:26 -0700, Jeff Liebermann <jeffl@xxxxxxxxxx>
wrote:

On Fri, 02 Oct 2009 09:15:31 +0800, who where <noone@xxxxxxxx> wrote:

On Thu, 01 Oct 2009 09:34:43 -0700, Jeff Liebermann <jeffl@xxxxxxxxxx>
wrote:

On Thu, 1 Oct 2009 14:29:37 +0100, "N_Cook" <diverse@xxxxxxxxx> wrote:

How to store to retain it for possible future use?

<http://en.wikipedia.org/wiki/Lithium-ion_battery#Shelf_life>
Store at about 50% charge in the coldest place you can find. Warm to
room temperatures before using.

"At a 100% charge level, a typical Li-ion laptop battery that is full
most of the time at 25 °C or 77 °F will irreversibly lose
approximately 20% capacity per year...."

that's seriously dated and extremely inaccurate. It doesn't explain
the packs that are ten years older (or more) and still can demonstrate
2/3rds of original capacity. Unfortunately some of these references
seem to never track reality.

How recent a web page would you consider to be adequately up to date?

More pages that say basically the same thing:
<http://www.batteryuniversity.com/parttwo-34.htm>
<http://powerelectronics.com/portable_power_management/battery_charger_ics/proper_care_extends-li-ion-battery-0425/>

<http://www.apple.com/batteries/>
If you use your iPod, iPhone, or notebook in temperatures higher
than 95° F (or 35° C), you may permanently damage your battery?s
capacity. That is, your battery won?t power your device as long on
any given charge. You may damage it even more if you charge the
device in these temperatures. Even storing a battery in a hot
environment can damage it irreversibly.

<http://www.centralhobbies.com/instructional/lithium.html>
3. Don't charge up the battery pack just to store it away. When
storing for long periods of time, keep the battery at a 40% charge
level.

More if you want them.... Google for "Li-Ion battery care".

You've rolled a number of points into one. I was referring
speciically to their 20% p.a. loss of capacity claim, which is a
crock.

deliberately discharged and then unattended outside of pc

That will blow up the battery.

That's also an extreme view, assuming discharge to the "normal"
end-point and *not* to zero volts per cell (which is geberally
precluded by the pack protection module anyway).

Agreed. However, the OP didn't specify how he plans to discharge the
battery. I had visions of discharging the battery pack outside of the
laptop (or whatever).

If it is a laptop pack recent enough to care about, it will contain a
pack protection module which will preclude discharge beyond a LVCO
point, typically 3.0v, and will also preclude excessive discharge
current. Nothing unsafe about a DYI discharge on that pack.

If it is a single cell from a cellphone or similar, different story.
these tend to have minimal inbuilt protection (if any) and rely
heavily on the host device for the customary protective functions.

Have you ever witnessed that occur? The normal decomposition of cells
allowed to deteriorate from EOD is non-spectacular, just a quiet
process without the leakage that say an alkaline primary would
exhibit.

Witnessed what? Having a Li-Ion battery die from excessive discharge?
Yep, but with LiPo batteries in model airplanes. They don't have the
protection found in most laptops and cell phones. The motor is fully
able to fly the battery into the ground. Two to perhaps five such
cycles is all that's required to kill the battery.

No protection means all bets are off.

charged up in pc and then unattended outside of pc

Full charge will eventually self-deteriorate the battery.

The things that determine the rate of loss_of_usable_capacity are
temperature and state-of-charge. Also simple choices (not generally
available to the user of consumer appliances) play a big part in cycle
life. Lowering the end-of-charge voltage from 4.20 to 4.10 returns a
trebling of cycle life in return for a small reduction in usable
capacity.

I had the opportunity to verify part of that on a small scale. Four
identical LiPo batteries.
1. 100% charge refreshed every two weeks at room temperature.
2. 100% charge refreshed every two weeks in my fridge.
3. 50% charge refreshed every two weeks at room temperature.
4. 50% charge refreshed every two weeks in my fridge.
Unfortunately, 50% charge was largely a guess and my not have been
accurate. The 2 week interval was also not exact. None of the
batteries were discharged with any load other than self-discharge.

At the end of 6 months, I used a West Mtn Radio battery analyzer to
see what was left.
<http://www.westmountainradio.com/CBA.htm>
I returned all the batteries to room temperature, let them stabilize
for a day, and charged them all to 100%. I then tested them and
generated discharge graphs at rated Amp-Hr capacity.
1. 60% of rated capacity
2. 85% of rated capacity
3. 98% of rated capacity
4. 98% of rated capacity.
The above numbers are from my fading memory and may not be exact. I
think I can post the corresponding graphs, if I can find the data. The
laptop I was using for testing crashed and I'm not sure if I had
backed up the data.

No need. I've seen numbers on these before, and Evgenij Barsukov has
posted comment on this previously in sci.chem.electrochem.battery.

charged via otherwise unused pc once a month? 6 monthly ? yearly ? and then
removed from pc

Nope. Lifetime is measured in charge cycles. That would just
decriment the number of charge cycles available.

It isn't that simple.

True. It never is that simple.

stored in a fridge? or just a cool dry place or a warm place

Cool. Cold is better, but don't freeze. Optionally store in sealed
plastic bag to prevent condensation when removed from fridge.

So, since you indicate that everything I posted is wrong, how should
one store a Li-Ion battery?

I never suggested that everything you posted is wrong, far from it.
But several points were amiss and they attracted specific comment.

I have seen numerous manufacturer-derived articles recommending 50-60%
SOC and cool/cold but not freezing as the optimum storage condition
for maximised life. I see nothing at all wrong with this approach
*if* maximum life is the sole objective. If OTOH the user wants to be
able to pull the cell/battery out of storage and into service without
an intervening warm-up or recharge, maybe a higher SOC is warranted.
Like many things relating to Li-XX cells, it is a tradeoff.

The extra life obtained by reducing the EOC voltage is well documented
and well worth it in laptop applications BUT the end user doesn't get
to choose. The manufacturer is out to deliver (well, promise) the
maximum discharge runtime he can, and he doesn't give a rats how long
the pack lasts in service.

I have a pack from an olde Acernote Lite 370 series dated 9637, so it
is just over 13 years old. It is stored with, but not *in*, the
machine. About once every year or so I pull that out and run it until
the machine shuts down, then recharge it to 100% (sic). It delivers
about 1.3 hours, compared to 2.5+ when new. That is stored at 100%
and room temperature (32S/116E).

I also have several test packs of 18650 cells left over from a project
about five years ago when I designed a commercial Li-XX charger. They
were shelved at 4.20v and currently all are above 3.9v. I haven't
bothered to measure their storage capacity because I have no reason,
but I can assure you that they wouldn't show that sort of cell voltage
if they had lost 20% of original capacity per year.
.

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