The test data here shows how imbalance can grow over time as the cells are repeatedly cycled. The data shows the individual cell voltages of 3 cells in a 3-series pack. Two cells are very closely matched – see the green and yellow traces that look almost like a single trace on the graph. The third cell is at a lower voltage, shown in pink. The pack is shut off whenever any cell falls to 3.0V, the minimum safe voltage. So for each discharge, the pink cell will be the reason that the battery dies. From the data it can be seen that after discharge the voltages of all cells recover as this pack is not as badly mismatched as the failed 6-cell which was previously shown. Each time it is recharged however, the two strong cells reach the full level before the weak cell does. The two strong cells actually start to go into the overcharge range before the overcharge safety circuit interrupts the current at about 4.25V per cell for the strong cells. But at this point, the pink cell is not even full. So, on the next discharge, it already starts off behind the others, and once again is the first one to be drained and force a system shutdown. As the charge/discharge cycling continues, the weak cell continues to get weaker because it is charged up to a lower state of charge each time. When cells are operated in an unbalanced state, the overall pack performance will suffer, and the stronger cells may be subjected to overcharge abuse as shown here.