With a Digital Multimeter (Volt Meter) set to DC Volts, measure the cell balance. The nickle straps are good test points. Note the cell voltages.

Cell 1: TP6 to CL1

Cell 2: CL1 to CL2

Cell 3: CL2 to CL3

Cell 4: CL3 to CL4

Cell 5: CL4 to CL5 (Battery Pos)

The cell voltages should be in the range 3.0V to 4.2V. The cells should all read about the same, say 3.9V. If the cells are more than 0.1V different, then cell imbalance could be a problem for your battery pack.