Lithium battery packs and their chargers are rather fickle.
Almost all multiple cell battery packs have built-in electronics that check the state of the battery and might inhibit charging if they sense something wrong. The reasons is that charging a damaged battery may result in Bad Things Happening, i.e. fire or explosions.
Back in the days of NiCd battery packs replacement of a single dead cell might have been acceptable as a stop gap measure, but those battery packs were simple compared to their modern LiIon cousins.
My considered opinion would be, replace the battery pack, scavenge the good cells from the old pack and keep them for non critical single cell applications e.g. powering LED flashlights.