Just take a multimeter and and check each cell (one multimeter wire to minus other to
pluss of each cell).
There is no wrong wire, you can even put minus wire from multimeter to cells pluss, and + to -, it will just show your reading number with minus. In other words do not care too much about polarity of your multimeter it will read anyways!
So check each cell, so one connecting point is on outside of pack other in thr center. Check and see witch cell is damaged.
But maybe just nickel strip is damaged!