[Thinkpad] TP600 Battery Pack problem

[Steve Carter]

The built-in smart charger for the TP600 battery pack 
appears to be a fairly sophisticated microprocessor-based 
controller.  You can see the crystal in several of the photos. 
One of the surface-mount ICs appears to be a micro-controller, 
and there are a lot of other supporting integrated circuits. 
    
The problem they (IBM) are trying to solve is that in any series 
battery, some cells age faster than others. The hottest ones 
presumably age more rapidly, as James pointed out.  But they 
all age, even when not being used -- especially Li-Ion cells. 
    
At the end of useful battery life, the cells that have lost the 
most capacity (i.e. aged the fastest) become overcharged when 
trying to charge the remaining cells -- they're all in series 
and the same charge current flows through each cell. 
  
But here's the catch: 

Li-Ion cells can and have explode(d) when overcharged.  It seems that 
they when overcharged they evolve metallic Lithium, which is hugely 
reactive, and this results in a spontaneous reaction, or explosion, 
euphemistically called "venting with flame" by the cell manufacturers. 
     
On the NASA's Mars Rovers, which have 8 Lithium-Ion cells in series (!), 
the design team created eight individual battery-bypass circuits to prevent 
weak cells from being overcharged.  Hopefully this technique will extend 
the life of the battery packs, since there is no opportunity to replace 
the cells once launched.  The Maytag repairman doesn't make house-calls  
to deep space.   :-)  

It seems unlikely that IBM went to this extreme in the design of their 
battery pack for the TP600 series.  What the word-of-mouth evidence 
seems to indicate is that after, perhaps 300, full (~80%) discharges the 
charging circuit is deliberately disabled to prevent a liability situation. 
IBM is often said to be a company run by lawyers, as you may have heard. 
      
None of this helps you with your quest for the schematic, but it would be 
a significant task to reverse-engineer the schematic from the hardware, 
and you would still have to reverse-engineer the firmware (programming) of 
the micro-controller.  Having done this, you would then have to figure out 
how to re-program the controller for new cells.  In the end, the solution 
might be fairly simple, but getting there could be a long journey.  

There are replacement TP600 batteries available from non-IBM (Taiwanese ?) 
sources, so someone may have already gone to the trouble to do this. 
It seems doubtful (not to their economic advantage) that they would 
consider releasing the results of their work.   

I don't want to "rain on your parade", but rather just share what info 
I've gathered.  I hope you find some of this (way too-long) message helpful. 
                                 
++++++++++++++++++++++
On  Wed, 03Dec03, James McKenzie wrote, in part:
>From: James McKenzie <jjmckenzie51 at sprintpcs.com>
>To: David Gemmell - VK4GL <david.gemmell at optusnet.com.au>
>
>David:
>I don't think the problem is with the PCB, but rather with the placement 
>of the battery in the Thinkpad.  When I disassembled a 'dead' battery 
>for the 600 series, I found that the two cells closest to the CPU 
>(and a great source of heat) were "fouled"  and would not take a charge.  
>The other cells in the battery were just fine and continue to take a 
>charge.  I could rebuild the battery with new cells and I would expect 
>the 'new' battery would last as long as the 'old' battery.
>
>However, I don't know of a source for the schematic for the PCB. 
>Maybe, someone on the list can locate one.   >James McKenzie
>   
>     
>David Gemmell - VK4GL wrote:
>>I had seen that site, some excellent info, 
>>but I was really after the schematic of the PCB 
>>in the batt case to see where the design was astray.
>>
>>----- Original Message ----- 
>>From: "James McKenzie" <jjmckenzie51 at sprintpcs.com>
>>
>>>There was a lengthy discussion on rebuilding 600 series batteries.
>>>Look at the following site as it has instructions on how to rebuild 
>>>Thinkpad 600 series batteries:
>>>
>>>http://www3.sympatico.ca/milnoc/TP600Battery/
>>>
>>>It provides a great wealth of information on the 600-series 
>>>battery  problems and links on how to rebuild them. >James McKenzie
>>>
>>>
>>>David Gemmell - VK4GL wrote:
>>>>After reading many of the postings on TP600 battery pack 
>>>>problems, I would like to have a go at repairing mine.
>>>>
>>>>And - please - I do understand all the warnings about this - 
>>>> (the sky will fall in  - etc etc,)
>>>>but I do have the required knowledge and equipment.
>>>>
>>>>Does anyone have a SCHEMATIC of the charge control 
>>>>circuitry which is built into the battery pack?
>>>>Thanks David
>>>>________________________