Depending on the IBM/Lenovo computer, it will only charge the battery when it gets to a certain point of being discharged. Some of the earlier models don't charge at something like 90+% and the newer ones may have settings on what percentage you would like it to not charge.
It does this because the batteries that the computers use have a certain limit on charge/discharge cycles. So the computer doesn't charge the battery unless it needs to be charged. For example, if you unplug your computer to move to another room, and then plug it back in. That would be discharging the battery slightly and then start to charge again. It tries to avoid things like that to extend the battery's life.
This possibly could be what happened to you. I don't know since I don't know the specific situation with your computer.
Hardware Support Specialist