Measure the voltage of the battery, but don't use the battery yet. Just let it rest for several hours, and, next, measure the voltage again to find out if there's any damage inside the battery that you should worry... usually such as small nick means it's still safe to use... but if the condition of the shrink wrap gets worse as you continue to use the battery you may eventually short circuit the battery (worst thing that could ever happen) so as others have stated you could consider either fixing it with a very small amount of super glue or replace the shrink wrap altogether if that's what you prefer (or simply take extra care not to let it grow worse... which is what I do).