Lithium battery packs can sometimes stop working all of a sudden. In this video, I tried to revive the battery pack (it didn't work for this pack) and salvaged the remaining good cell from the pack before sending the rest for recycling.
18650 lithium battery packs are often found inside power tools, vacuum cleaners and other high powered devices. They are tiny potent powerhouses that would serve well in many DIY projects and are worth salvaging.