"BillW50" <BillW50@aol.kom> wrote in message
news:h79g41$ft5$1@news.eternal-september.org...
> In news:3dWlm.208$1r2.112@read4.inet.fi,
> John Doue typed on Fri, 28 Aug 2009 19:27:59 GMT:
>> M.I.5¾ wrote:
>>
>> Snip
>>>
>>> The one thing I do know about Li-ion batteries is that regardless of
>>> how you store them, they don't like sitting around doing nothing. They
>>> have to be periodically used. Sitting around, the electrodes
>>> oxidise increasing the internal resistance. Under load, as the
>>> battery discharges, the volt drop can fool the monitor circuit into
>>> believing that the battery has discharged before it really has and
>>> it shuts the laptop down prematurely (giving a lower apparent
>>> capacity than the battery really has). The effect is non reversible.
>>
>> This is indeed my experience but it involves only one specifi battery,
>> so I would not generalize it.
>>
>> I decided to keep my old laptop connected all the time to avoid
>> forgetting to recharge the battery. Not very sensible, but losing a
>> $150.00 battery would not be either :-).
>
> I don't believe it is as bad as what M.I.5¾ describes. As I have 7
> laptop/netbook lithium batteries that has been sitting unused in a drawer
> for over a year now. So according to M.I.5¾ theory, the electrodes will
> oxidize increasing the internal resistance and have a much lower running
> time. I haven't seen this yet with my Palm IIIc, RC electric aircraft, or
> laptop/netbook batteries.
>
> So I will try to test all of these batteries this weekend to see if any of
> the capacity has dropped in all of this time. This problem, if it exists
> should be clearly seen with the RC equipment. Since they use many more
> amps than laptops does and even with 100% capacity left, they only have
> about 10 minutes of running time. And if the internal resistance goes up
> in the least, the power drops off greatly and the running time will drop
> off very quickly. So we will see. They haven't been used in a year either.
>

It's fair to say that any effects are likely to vary from one battery to the
next (and I did suggest this). The storage advice is presumably intended to
keep a worst case battery alive as long as possible. In the real world, I
too am aware of batteries that seem to have a far longer life than others
despite being treated in worse ways. The one thing that doesn't seem to
vary though is that generally laptop batteries seem to require more care and
attention than batteries in other products. This may be because laptop
cells have a higher capacity than in many other products and there certainly
is a limiting factor at work on cell sizes, which is why laptop batteries
are frequently made up from series/parallel sets.

"BillW50" <BillW50@aol.kom> wrote in message
news:h79mkl$o9q$1@news.eternal-september.org...
> In news:4a9792d2$1_1@glkas0286.greenlnk.net,
> M.I.5¾ typed on Fri, 28 Aug 2009 09:18:36 +0100:
> [...]
>> Leaving the battery in a laptop while running on AC can shorten the
>> battery life, but not for the reasons often cited. It is the
>> internal heat generated by the laptop warming up the battery that
>> actually shortens its life. Laptops do this to varying degrees
>> depending on the internal arrangement of the heat producing parts.
>
> Well besides the heat thing, I have a different theory on the rest if heat
> isn't a factor. As you can have a laptop and not use it for years and just
> keep it on AC and with the battery in. And in many cases, the battery will
> only trickle charge when the battery drops down to 96% capacity and
> trickle charge it back up to 100%. Many of them will repeat this cycle as
> long as the battery stays good. And there is no heat to speak of, yet
> these same batteries still goes downhill much faster than leaving them in
> a drawer (except for John's).
>
> Yet my Palm IIIc has been sitting on the charger for the past 5 years on
> this same battery and no detectable loss of capacity at all. Everything
> should be exactly the very same conditions right? Nope! There is one
> slight difference between the two. The Palm only charges the lithium only
> up to 4.10v per cell while almost all laptops charge them up to 4.2v per
> cell.
>
> So it is my opinion coupled with my experience that charging lithium
> batteries up to 4.10v per cell doesn't really harm them, but 4.20v per
> cell really shortens their life greatly. And this is still keeping the
> battery cold. Add the normal use with all of the extra heat and no wonder
> a battery can die in a couple of years even though you never used it on
> battery power ever.
>
> Why do laptops manufacture charge them too high IMHO? The answer is easy.
> One, they can brag slightly longer running times. Secondly, they know you
> will need to buy an expensive battery which they can make a lot of money
> by selling you one.
>

It's a bit more complex than that. Floating them at 4.20v per cell is
perfectly OK. Floating them at 4.22v per cell will attempt to overcharge
them by 25% with the resultant damage that will cause (often cell rupture).
Designing a charge circuit with that sort of accuracy is moderately
difficult (but not that difficult). Some manufacturers will go for the
cheaper option of using a lower target voltage which can then be implimented
with much relaxed tolerances (and of course the attached cost savings).
Thus your Palm will have an almost zero chance of battery damage if the
voltage is a percent or two too high, but the price paid is that battery
will never charge to more than around 70% of its capability.

>> The advice about discharging to 40% and storing in the fridge abounds
>> everywhere, but it seems to have zero provenance. Part of the
>> problem is a reticence on the part of the battery manufacturers to
>> provide an authoritative guide as to how to treat their batteries.
>
> I believe the percentage of the capacity isn't very meaningful at any
> rate. As I believe what you are using as a gauge of 100% is more
> important. As what is the voltage per cell at 100%. Then and only then you
> can judge what 40% really is.
>

The voltage per cell at 100% charge is 4.20 volts. This is fixed by the
chemistry and not some end user. 40% charge is 3.77 volts in Li-ion
chemistry and 3.86 volts in Li-ion-Poly (Both assuming that 2.80 volts is
the end point - though most manufacturers will cut the discharge off at 3.00
volts for good reasons). Some older Sony designs are an exception to this
as they have a lower end point voltage.

>> The best advice that I have been able find is that batteries that are
>> removed from a laptop while operating on AC power should be kept
>> anywhere from 30% to 100% charge at not more than 25°C (77°F) but
>> ideally below 20°C (68°F). They should be periodically discharged
>> and charged, at intervals ideally not exceeding about 45 days
>> (opinions vary from 30 to 60 days so I have plummed for the mean). I
>> have several batteries that exhibit near their full rated capacity
>> after 15 years of such treatment (and some of those discharge/charges
>> sometimes got missed for a few months).
>
> Well I haven't seen any evidence that lithium batteries need to be
> exercised every 30 to 60 days. But then again my lithium batteries only
> last for 10 years and not 15 either. I'll do some testing this weekend on
> a bunch of lithium batteries that has been sitting in a drawer. And
> hopefully I'll see some evidence of this.
>

Difficulty is: that as I have said, the manufacturers are reticent to
publish much information on their batteries. That Li-ion batteries
deteriorate through non use is clear - there are plenty of examples. As I
have stated above, the effect from different manufacturers, and even
different examples of the same design, varies considerably. Some will
survive with only moderate use, while others require frequent use. The
problem is that impurities in the chemistry causes the electrodes to oxidise
while not in use. This oxidation raises the internal resistance. The rate
of oxidation is a function of the impurity level (and of course what
impurities are present) which can vary considerably between examples

>> On the other hand, a colleague of mine stored his laptop battery
>> partially charged (yes, 40%) in a fridge for 2 years and was
>> initially delighted when his battery monitoring software (BattStat on
>> his laptop) reported 97% capacity. However, it quickly revised its
>> opinion to 68% once he started to charge the battery (I presume the
>> monitor circuit inside the battery did its stuff at this point). I
>> know this is only one example, but you can't help wondering.
>
> Yes capacity programs really don't know the capacity until they are
> calibrated for the individual battery. And even then it is questionable
> depending on how it calibrates itself. What is far better is just using
> them and checking the running time. Doing this three times seems to work
> best as the first time tends to have the longest running time measurement.
> The next two seems to give you a better measurement of the real running
> time and capacity of the battery in question.
>

Actually, that isn't correct. The *state of charge* of a Lithium ion
battery can be precisely measured from the terminal voltage. Knowing the
chemistry, it is one factor that is fixed and is predictable (unlike most
other battery types). What can't be instantly determined is the capacity
remaining in the cell. This can be determined by the reduction in voltage
as the cell discharges (knowing the current being drawn, the time elapsed
and the voltage/charge curve), but this obviously takes a short time to
determine for a battery that is unused for a while. Knowing the true mAh
from 100% charge to the end point provides an accurate picture of the
battery's remaining capacity (which is what the calibration cycle does).
The problem with all this is that if the cell has any oxidation from
standing idle, then the resultant terminal voltage will be lower than the
battery real voltage (its e.m.f.) fooling the monitoring circuitry,

>> The one thing I do know about Li-ion batteries is that regardless of
>> how you store them, they don't like sitting around doing nothing. They
>> have to be periodically used. Sitting around, the electrodes
>> oxidise increasing the internal resistance. Under load, as the
>> battery discharges, the volt drop can fool the monitor circuit into
>> believing that the battery has discharged before it really has and it
>> shuts the laptop down prematurely (giving a lower apparent capacity
>> than the battery really has). The effect is non reversible.
>
> I'll experiment with a bunch of batteries that has been sitting for a year
> that I know what the real capacity was for each just a year ago. And I am
> expecting about 5% loss per year in capacity kept in this state of sitting
> in the drawer.
>

You may find 5%. You may find substantially different figures. I presume
that you don't know what their internal resistance was a year ago. A pity
because it would be useful to know how much it has increased.

What results you do get will all depend on the individual batteries but your
sample is probably not large enough to make any definitive judgements.

"BillW50" <BillW50@aol.kom> wrote in message
news:h7enhh$aee$1@news.eternal-september.org...
> In news:4a9792d2$1_1@glkas0286.greenlnk.net,
> M.I.5¾ typed on Fri, 28 Aug 2009 09:18:36 +0100:
>> ... They should be periodically discharged and charged, at intervals
>> ideally not exceeding about 45 days (opinions vary from 30 to 60 days so
>> I have plummed for the mean). I have several batteries that exhibit near
>> their full rated capacity after 15 years of such treatment (and some of
>> those discharge/charges sometimes got missed for a few months).
>> On the other hand, a colleague of mine stored his laptop battery
>> partially charged (yes, 40%) in a fridge for 2 years and was
>> initially delighted when his battery monitoring software (BattStat on
>> his laptop) reported 97% capacity. However, it quickly revised its
>> opinion to 68% once he started to charge the battery (I presume the
>> monitor circuit inside the battery did its stuff at this point). I
>> know this is only one example, but you can't help wondering.
>>
>> The one thing I do know about Li-ion batteries is that regardless of
>> how you store them, they don't like sitting around doing nothing. They
>> have to be periodically used. Sitting around, the electrodes
>> oxidise increasing the internal resistance. Under load, as the
>> battery discharges, the volt drop can fool the monitor circuit into
>> believing that the battery has discharged before it really has and it
>> shuts the laptop down prematurely (giving a lower apparent capacity
>> than the battery really has). The effect is non reversible.
>
> Well I did some tests and here is what I have. All but the first one was
> sitting in a drawer unused for over a year. The figure in the parenthesis
> is what it should be being brand new.
>
> EeePC
> WiFi on, playing audio, screen at 24% brightness
>
> WHT-XXX-XX-XXXXXXXXXXXX 10440ma 7.4v 330 min
> WHT-702-8G-XXXXXXXXX709 5200ma 7.4v 164 min (184 min)
> WHT-702-8G-XXXXXXXXX193 5200ma 7.4v 162 min (184 min)
> BLK-701-4G-XXXXXXXXX125 5200ma 7.4v 162 min (184 min)
> BLK-701-4G-XXXXXXXXX973 4400ma 7.4v 115 min (152 min)
>
> I really don't see any evidence that you should exercise them every 45
> days otherwise the electrodes oxidize. I have heard the same for lead-acid
> batteries too. Although I only can make lithium batteries last 10 years
> and not 15 years. So your mileage may vary.
>

Most around an11% reduction in capacity (the worst was just under 25%). You
are right that there is no evidence that exercise would alter the results
because none were subjected to this. However, even an 11% reduction is IME
a large loss in capacity for such batteries. It is a pity that you didn't
have a control group regularly charged and discharged over the same period
of time as that would answer the point.

However, there is one pointer. You can make them last 10 years by doing
nothing. Mine last 15 years with an occaisional charge/discharge (which
they get from actually being used). Hmmm.

Lead-acid batteries don't oxidize - they sulphate. A totally different
effect from a totally different chemistry.