Battery Loss Rate

[z.entropic]

[quote="Leon"]ok, one last (for now :-)) follow-up... accepting what you said about deep discharges not being bad under normal circumstances, all things created equal, is it even marginally better to do shallow vs deep discharges, or entirely equal over time?

Also, while the Dr. isn't charging ;-), do you recommend long term storage in the fridge or freezer, and at what charge level?[/quote]

It's better NOT to deep-discharge too often (the active materials expand and contact as the lithium is moving in and out of the structure, resulting in a phenomenon called electrochemical grinding which results in the loss of electrical contact, loss of capacity and an increase in cell impedance), but, as some posters correctly stated, you have to do it from time to time to recalibrate the coulomb (charge) counter. The optimum range seems to be between 30 and 70 % SOC, this is what satellite power engineers came up with, and I would tend to believe them--they have much at stake up there!

I already mentioned that the best way to store a Li-ion pack for longer periods of time is at 50 % SOC at moderately low temperatures, but not in a freezer! Make sure that the pack is well insulated against water; include a bag with an activated desiccant (a water absorbing powder or granules such as those used to remove humidity in basements).

Some people in this field, including myself, believe that it's not only the cycling that defines the life span of Li-ion batteries, but that they have an inherently limited lifetime even under optimum storage conditions.

According to the laws of thermodynamics and electrochemistry, Li-ion batteries should not be possible at all as the electrochemical systems used are inherently unstable (they tend to react by themselves and don't need any external energy input to do so). These batteries are only possible because of the many passivation phenomena occurring on both electrodes which decrease the rate of all those harmful reactions (slow kinetics).

z.entropic

[Leon]

Well, even after being in the Computer Industry for over 15 years, and with both CS and EE Degrees, I still find a good amount of magic in technology and my Thinkpad. Now, it's nice to know there is some magic in my battery too!

Thanks very much z!

According to the laws of thermodynamics and electrochemistry, Li-ion batteries should not be possible at all ....

[beeblebrox]

Just want to add my experience here.

Being myself an EE/CS engineer and having studied a lot of literature about battery technology I did a test of a few battery packs (T20 batteries):

On my T20 I hardly ever used the battery, it was plugged in all the time (as recommended on some pages). After 3 years it had about 25 cycles (never deep cycled, never reconditioned). It lasted about 3-3.5 hours still. Battery maximizer told me it needs to be conditioned and deep charged because it showed misalignments in the meter. I checked a few battery webpages for advice and did the deep charge.

The battery died. It suddenly had only 10Wh instead of 34Wh. A test showed that after 10 minutes it collapsed from 95% to 5% and then stayed alive for about 5 minutes. Ok. this is a sign of an internal short cut within a battery pair of cells.
I started reconditioning several times. Same results, however the meter told me 2 minutes left, which actually became 45 minutes. Since the battery is gone anyway, I am using it now happily without thinking about the "waste of battery life".
I constantly get 45 minutes (decreasing). The meter is quite precise after a while.

So in conclusion, deep charging the battery (less than 3%) kills it. Do not go below 10%, always keep the battery charged, despite the power meter becoming somewhat unreliable.

Second test:
Brand new battery pack of a T40p. Knowing, that batteries are heat sensitive, the pack (never used, 3 cycles) stayed in the fridge for a year now (I should have sold it!!) with about 40% charge.
A quick test: it has lost 4% capacity. Which is within error limits, because it has never been conditioned.

[plasdom]

In less than a month of use, my battery capacity has fallen from the usual 47.XX to 43.XX. I get on average 2:15 hours. This is a brand new thinkpad 2378

[Leon]

beeblebrox-
unless I'm mistaken, your experience is consistent with Z's information. You seem to indicate that the evidence shows the battery had a "sign of an internal short cut within a battery pair of cells". So, I believe a slight adjustment in your conclusion is applicable for accuracy (in bold). "deep charging the battery (less than 3%) kills it in cases when it may have an internal short. Since there is no way to predict this, it should be avoided. Agree?

plasdom-
How many cycles on your battery?
Welcome to our Forum. Please add Location and other pertinent information to your profile. Not required, but appreciated.

[rivalarrival]

Seems I'm kinda lucky I didn't blow my T22 and myself to kingdom come. Regardless, something screwy happened when I chilled the batteries at about 90% charge and then tried to continue charging them. The cells accepted much more charge time than I had expected before finally "topping off"

The next dischage cycle (at ambient temps) and they gained 20 percent of their charge each. Mind you, these were old batteries, which is why I was screwing with them. I had to discharge them completely, again, at ambient temps, to verify what's going on, but they both appear to have stabilized at the higher capacity, and the annoying habit they had of dropping off at 20% has been eliminated.

To be honest, I understood about 75% of z.entropic's last post; I think the important parts were don't freeze your batteries or they'll explode

I can't argue with the results I'm seeing, but I am worried that freezing the batteries may cause them to do nasty things in the near future... I dunno...

[z.entropic]

rivalarrival, it took much longer to recharge your chilled battery because its internal resistance significantly increased. The reason behind it is easy to understand if you know how exctly Li-ion batteries are charged. The method is common to ALL Li-ion batteries and packs, so let me explain it in some detail.

The Li-ion battery charge protocol used by everybody is the so-called CC-CV method, or taper current, method (CC-CV stands for constant current, then constant voltage). A cell, or pack, is charged with a constant current at a rate of between 0.7 to 1C (the unit of C is inverse of time, i.e., hours)^(-1), so a C/2 rate means a current value, in amperes, numerically equal to to the 1/Q, where Q is the capacity in ampere-hours) until the cell voltage hits 4.20 V, and then the current is continuously decreased to maintain the same, constant voltage until the current reaches some small value, like C/10 or even less.

The second rule in charging Li-ion batteries is that the individual Li-ion cell voltage should never, but never, be raised to higher than 4.20-4.25 V during charging. Why? Because the positive electrode active material used in 99.99% of commercial Li-ion cells has a 45% higher charge capacity than normally used, that is, you can actually extract that much more lithium. However, when you do this, the delithiated Li(1-x)CoO2 (that is, the now-charged material from which lithium ions have been extracted/'pulled out') becomes chemically unstable as the charged layered-cake inorganic material structure has a tendency to collapse without all the lithium-ion 'cream' layers in between the cobalt and oxygen atom layers. When it collapses, it releases the excess oxygen ATOMS, O., not molecules, O2, a so-called singlet oxygen. Now, this oxygen is extremely reactive (they are in fact free radicals, that is, have unpaired electrons) and is being released into the solution of flammable organic solvents making up the electrolyte solution. In effect, you are starting internal combustion system in the cell... Once again, this is why the upper cut-off voltage control in lithium cobalt batteries is so critical to their safe operation, but if a charger fails and the voltage is increased to over 4.2 V, you may be in for a big problem.

There is another, related reason not to overcharge these batteries. For weight and capacity reasons, the amount of graphite or other carbon on the anode (negative) side of each cell is just a bit higher than necessary to accept all that lithium moving from the cobalt oxide-based cathode, maybe 5-15% excess. Now, you may remember what I said above, that there is a ~45% excess of lithium available in the cathode as compared to the amount taken out at 4.2 V, so where is it going to go if there is not enough space in the graphite anode? It will plate on the anode in the form of a very reactive mossy lithium powder which I have already mentioned in one of my previous posts. Thus, another potential problem on top of the instable cathode.

Did I scare enough y'all ? But, seriously, these two situations are no joke at all and, in fact, you read about them from time to time in newspapers...

z.entropic

[benplaut]

(this is probably the shortest post in this thread... )

i thought it might be usefull just to check in and see if my battery is about at what it should be...

the MaxiMiser shows %100, and when in Battery Health, it shows that i have

Full Charge Capacity: 48.16 Wh
Design Capacity: 47.52 Wh

Cycle Count: 16

i hardly use the battery for extended periods of time, and mainly just switch between two mini-docks... so the low cycles make sense.

the TP is a T40 with the standard battery... I bought it off Ebay so was unsure on the Battery's condition, but it appears to be good

[rivalarrival]

Appreciate your insight, z.entropic... You da Man!

[plasdom]

Leon,

Design Capacity: 47.52
Full charge capacity: 43.48
Cycle Count: 19 (what is this anyway?)

[Leon]

Cycle Count is the equivalent of how many "Full Cycles" your battery has had. Remaining capacity sounds a little low. My battery is 9 months old, 166 cycles, 39.43 remaining.

[plasdom]

As soon as I unplug it, the remaining capacity drops from 100% to 97% -96% immediately.

[plasdom]

Against the advice in this thread I just reconditioned and capacity dropped immediately to 43.28

[rivalarrival]

If the battery meter becomes inaccurate, which we have strong reason to believe it does, deep cycling the battery is going to reset the meter, giving a more accurate reading...

Deep cycling, I believe, doesn't CAUSE the battery loss, it REVEALS the loss.

If you're losing capacity continuously, and the meter is never reset to the actual value, after a deep cycle you're revealing all the loss the meter didn't show over time.

After my first deep cycle, I did lose a few Wh, after the fourth, I was back to my starting state, but the meter was accurate all the way from 100% to 0% (it used to drop from 30 to 5 instantly)

[jusa-]

Hi!

I bought new IBM T40 laptop. My battery's full charge capacity is only 42,16 Wh and design capacity is 47.52 Wh. Cycle count is 1. Is this normal or should I ask new battery from IBM? My laptop is manufactured in December 2004, but battery is manufactured in September 2003.