Recondition

[fixup]

I got an old 3600mAh battery and my X20 alerted me an empty battery less than an hour. So, I thought I should recondition it.

I let it keep running. At the end it did not go standby as the IBM tips suggested but went off like a sudden power failure. The capacity went down to 25.60 from 36.50. Ouch!

I read somewhere that I might need to do it 3 times. So I did it again and capacity went down to 20.48. Crap!

Then I did it the 3rd time, now it is only 13.12!

I know that Li-Ion should not go lower than 3% otherwise the battery will hurt permanently, but IBM says I must go lower than that for reconditioning at least every month. What gives?

So, my question is: do I really have to go lower than 3% to get a correct reconditioning? What about 4% or 5% that's relatively safe?

[ajkula66]

It seems to me like you have one or more bad cells in that battery...and that reconditioning of any kind will do it no good.

[fixup]

Before I pour more time into these reconditioning, I really want to know: do I have to go lower than 3% as IBM said?

Update: After more recycles, I have got the following facts:

* If one cell goes down to 3V, discharge is cut off and machine is down off of power.
* If one cell reaches up to 4.2V, charging is stopped.
* Capacity is exclusively mapped to voltage: 0% capacity is 10.5V, 5% is 10.625V, 90% is 12.5V and 100% is 12.65V.
*The weakest cell defines the capacity of the battery package.

So, if one cell somehow (e.g. not used for a long time) becomes 0.1V or lower than other cells during discharge, other cells won't be fully discharged. This cell will also be likely to reach 4.2V before other cells are fully charged. The result: the battery package will have less actual capacity and cannot be fully charged.

If recondition such a battery below 3%, it can simply make it worse, because voltage difference will be even larger under deep discharge. As cells are not charged individually, things will go worse and worse.

Therefore, it is not a good idea to recondition below 3% for a battery that's already in bad condition. Recondition is mainly to achieve a more accurate gauge, not necessarily to recover capacity. If recondition is done above 3%, the gauge might not be as accurate as it could be, but at least there won't be further damage to the weakest cell.

To recover some capacity, I had to charge/discharge the weakest cell to make its voltage closer to other cells. I did not get much capacity back, but at least now it can be charged to 100%. Hopefully I'll get more capacity back after more cycles of use (this battery has not been used for a long time, only 76 counts). After I opened the case, I realized that I did not have to open the entire package - I only need to cut some holes with a Dremel:



What's showing in the picture is charging the middle cells. To charge the left or right cells, use the tips of the big black and red wires soldered on the PCB. As you can see, these terminals can all be easily accessed if you drill holes above them.

In conclusion about reconditioning: disable standby and hibernation timers but do set the alarm action to be "standby" at 3%. Keep the machine running on battery (AC unplugged) until it goes to standby mode, then plug in AC to charge it until the battery LED is solid green.

I was confused by the IBM instructions and disabled the standby alarm action at 3% and let the battery to be over (not just deep) discharged until one cell went down to 3V. After that my battery capacity went down to half. What a costly confusion!

Never drain the battery below 3% (10.5V), IBM's instruction is wrong!!!