This is some good info. From what I've read and see on other Videos too. I think that these principles could apply to other Types of Battery Packs too.
Jump starting a recelled IBM Thinkpad T40 battery
Replacing the cells on IBM Thinkpad T40's battery
Disclaimer: This is description of my personal project and not a tutorial. Lithium batteries can be dangerous, if they are not treated correctly. I take no responsibility if anyone decides to do anything described in this page. Safest way to get laptop with dead battery to work again is to use it without the battery, charger plugged in or to get a new battery.
I bought a used Thinkpad T40 this summer and I love how it feels. I was surprised when I took T40 out of the box and noticed how thin it is. The design of the body makes T40 feel lighter than it is. After initial testing I installed newest Ubuntu (11.04) in place of the Windows XP. I wasn't sure how long the battery lasts and how long installation would take, so I kept the charger plugged in. So far so good. I noticed one major problem when I tried to test the screen by watching few DVDs. I was lying on the couch and T40 was on my lap. I started VLC and opened the disc. Couple of seconds later T40 shut down without any warning. Unlike I first though, reason wasn't overheating, but instead the battery. I took the battery apart and made few tests with multimeter and 10ohm power resistor. Conclusion was that the battery wasn't able to output even 1A current, without the voltage dropping below 9.5V. Circuit inside the battery shuts off the battery when the voltage drops to about 3.1V / cell or combined 9.3V. I found out one of the three cell pairs was bad and rest of the cells kept almost the same voltage despite the 1A load. I replaced all six cells with "new ones", which might not have the same capacity as when they were new, but I was sure they could give couple of amps without problems.
- Replacing the Cells in Battery Packs
- Who knew Thinkpad batteries require a jump start? - Hack a Day
- Repairing T40's battery
- Revive your tired Dremel battery pack - Hack a Day
- Makita battery pack repair - Hack a Day
- Jump starting a recelled IBM Thinkpad T40 battery - YouTube