IBM ThinkPad T41 - battery repair(FRU No - 08K8201, 08K8199)

[wisdomkeeper]

Hello, fellows. I'm new to this forum, and firstly want to say one big "Thank you" for the all useful information in this forum, that helped me more than once. I've read the forum long time prior my registration here.
The purpose of this topic is to ask a question about the battery of my IBM T41 Thinkpad. It's old, but it serves me well. I've bought it about two years ago. The seller told me that the battery is brand new. Indeed, IBM Software said that it's OK - almost full capacity, no wearing. But after about 10 cycles of perfect performance(3hours+) the battery suddenly died and held no more than 10-15 minutes of charge. The situation became so bad, that sometimes when the mains blink for a moment, instead of switching to battery power, my laptop completely shuts off, as it is no battery at all. Sometimes it switches to battery power and provides me with some limited time.
I have knowledge of electronics, as well experience in repairing of computer systems, but almost no experience in repairing specially laptop batteries. I know that it could get tricky, so I want to ask for your help and experience in such matters, because I want to bring my battery back to life.
p.s I apologize for my not so good English, but i'm not from english speaking country, so I'm doing my best.
p.s2 Beware of 40gig Hitachi drives, found in the Thinkpad's of these years. I have two defective drives without S.M.A.R.T warning or any warning at all. They just suddenly became extremely slow, when I scanned with MHDD, after I've recovered any information i can, they shown slow and bad sectors. After day or two the sectors suddenly disappeared at all. After some time - appeared again, And so until complete death. I suppose it's problem with reading heads, due to technology flaw in manufacturing process.

[wisdomkeeper]

Is there anyone, who has tested/diagnosed/replaced cell/cells of the battery pack?

[axur-delmeria]

A quick google search yields this result: http://jaforeck.wordpress.com/2012/07/24/t40-recelling/

[wisdomkeeper]

Thank you, but is there a way to identify the faulty cell, without replacing the whole battery package, because it can get very expensive to replace the whole package. 6 high quality cells(18650) could cost more than half of the price of new "replacement" battery.
p.s I searched in Google before my post here, maybe I have chosen the wrong keywords.

[automobus]

ONG, is that all there is to it? Apply voltage to battery interface connector, brings Smart Battery back to life? If it just as simple for vintage ThinkPad smart battery? (such as 560, 570, 600…) I was under the impression that every laptop since 1998 is forced obsolete due to secret battery computer. This could change my world view!

[geka3250]

is there a way to identify the faulty cell, without replacing the whole battery package

Strongly not recommended! Cells must be identical as more as possible. Cells with different wear level/capacity can get high voltage difference while using a battery.
So prepare repack all cells with same capacity as original battery had.
BTW, repacked T43 battery. Have one working battery, but only 8W/h left and other - with normal cells(1-2 hours working) and freezed controller(shows 4.2W/h and dont want recalibrate). Disassembled them with screwdriver(applied some acetone on joints to make plastic more flexible there), unsoldered cells from "plus" to "minus", soldered good cells to good controller from "minus" to "plus". Got blocked battery without output voltage, but after applying charge battery became unblocked Doing recalibration proccess...

[wisdomkeeper]

Strongly not recommended! Cells must be identical as more as possible.

I know, but because the battery died suddenly and before it's death it provided more than 2 1/2 hours of battery life, I think that only one of the cells is faulty. This is why I think that it doesn't make sense to replace the whole package, beyond the fact that it's much more expensive. I've already opened my battery using screwdriver and knife.
If I replace the faulty cell, of course it would be with the same capacity cell as the original one.

[geka3250]

If other cells good you can try to replace fault cell, just make voltage similar on new and old cells(discharge or charge to equivalent voltage). BTW, what voltage on each cell parallel now?

[wisdomkeeper]

3.79V 3.73V 4.15V
Controller - Amtel ATMega 8A AU1013

[geka3250]

So you have 2 parralels some discharged and one fully charged. Try to charge each parallers with 4.2V(with current limited power source about 1-2A) until current drops to about 100mA to make equivalent voltage. After connect whole battery to load about 1-2A, measure each parallels - cells with lower voltage will be bad.

[wisdomkeeper]

First thing in the morning. Thank you. I have 900mА Power supply, that I think is close enough.

[wisdomkeeper]

Even after more than an hour on the charger, the charging current of the one of the cell couples stays about 1A, which is the limit of the power supply unit I use - 1A 4.5V. Indeed... there is something wrong with this battery. I thought it can be salvaged, now I'm not so sure.

[geka3250]

4.5V is very dangerous for Lithium! Be carefull - can do BAM!
4.25V is maximal charge voltage, 4.2 is optimal

[wisdomkeeper]

I will never try to charge it completely. Yes, it can explode, but the battery wasn't even changed it's temperature at all when charging. I was monitoring the voltage(and temperature) periodically. It seems that the couple with 4.15V(see my earlier posts) is faulty. I've used one 12V(8W) soldering iron as load after I charged the battery. The voltage of the other couples was stable, but the voltage of the cell couple in question very quickly decreases from 4.12V to under 2.9V. This is why my laptop wasn't recognizing this battery. I will see which is the bad 18650 cell and will replace it OR will replace both 18650-s. Because the voltage of the other cell couples was stable during the discharge(stable and higher than 4.12V) it seems that the other two cell couples are operative. The battery is from 2008year but with only 16 cycles, as reported from battery maximizer.
p.s Update - now when charging the faulty couple, one of the cells become a bit a little warmer than the other. Maybe this is the faulty cell. I will make no further attempts to recharge it.

[geka3250]

but the voltage of the cell couple in question very quickly decreases from 4.12V to under 2.9V

Yea, it seems the problem. Try to replace both cells there