You should add a relatively high current load (e.g. discharging the battery by a battery charger such as Much More Cell Master) to the battery and then check the voltage of individual cell.
If you don't have a high current load, the simplest way (but not so accurate) is to use a 540 motor connect to each cell one by one and check the cell votlage (e.g. if it drops to below 0.8 even after charging, the cell is probably death). This method could help to identify the very poor condition cell.
You should add a relatively high current load (e.g. discharging the battery by a battery charger such as Much More Cell Master) to the battery and then check the voltage of individual cell.