I think it is sad, if not a bit deceiving that Lenovo does not state the reason for the recall - these batteries can overheat, catch fire, and burn aggressively producing very high heat levels and noxious gases. Stating the reason, I believe, would motivate users to take advantage of this recall. Sadly, so many folks ignore recall notices if they feel (guess?) they do not have a defective product.
I note this also affects some Canadian systems too.
US-Consumer Protection Safety Commission: Lenovo Recalls Battery Packs for ThinkPad Notebook Computers Due to Fire Hazard