Lithium battery packs reaching the end of their life usually have a lot of kick left in them. That’s because they’re made up of multiple cells and it only takes the failure of one to bork the entire battery. One of the most interesting examples we’ve heard of this is in the Toyota Prius, but that’s a story for another time. In this case, [Mika] wanted to resurrect the battery from his IBM Thinkpad T40. He identified the offending cell and replaced it, but couldn’t get any juice out of the battery after the repair.
He was measuring 0V on the output, but could measure the cells instead of the control circuitry and was getting over 11V. Clearly, the control circuit wasn’t allowing an output. We completely understand the concept here (think about that really bad press about exploding laptop batteries). It seems there’s a lockout mechanism when the control circuit loses power. [Mika] managed to get past this by shorting voltage into the control circuit, a method he likes in the video after the break to jump starting a car.