I recently scavenged a laptop battery pack to see what sort of treasure was inside. I found a 3S2P 18650 pack with a PCB connected. I am only interested in the batteries for now, so I cut the PCB off and decided to investigate the batteries. I don’t own a battery analyzer, but I do own a power supply and a DVM. I measured the 3 sets, two were at around 3.5V, and the third was at 2.0V. I charged the pair at 2.0V up to about 3.7V and have let them sit. It seemed to me that it did not take many amp-hours to charge this pair up, so I paid a bit more attention while charging the next pair. I was able to add about 0.2V to the battery resting voltage in about 2 hours with a charge current of 0.27A. The original capacity of the pair should be 4 amp-hrs, and I added about 0.6A-hrs (a bit less) , or about 15% best case. I know the discharge curve of Li-ion is not linear, but roughly 0.8V is the usable voltage range, and to charge up 0.2V of that should take closer to 25% of the amp-hour rating, and that ignores any heating loss or other inefficiency.
Seems like these cells are likely no where near 2 amp-hour each any longer, which is probably why they got dumped. Is this a correct conclusion, or did I over simplify this?