# Application of Infrared Thermography in E-Bike Battery Pack Detail Analysis--Case Study
## 3 Analysis and Diagnostics of the Battery Pack
### Battery Cells Electric Parameters and Functional Analysis
Furthermore, the same figure (rightmost) shows the contents of the disassembled e-bike battery pack without 2 pack-origin defective cells and with 10 replacement cells acquired from the used laptop battery packs. Replacement cells from the used battery packs were originally planned to be a replacement source and eventually to replace all defective cells of the initial e-bike battery pack [40]. Among newly sourced cells, we found two battery cells that matched in appearance and labeled exactly as those in the original e-bike battery pack, so we placed them at cell positions 1 and 3 in the initial battery pack layout. With that substitution, the battery pack was restored back to the operational state, thus making the further investigation and analysis possible to continue and the battery pack usable again to some extent. Table 2 shows the discharge parameters of all cells that were previously charged to nominal maximum voltage of 4.2 V. The cells were discharged with current of 2 A to voltage of 3 V [41]. That specific value of discharge current is the value closest to finding the maximum capacity under real conditions and also the value expected for the maximum battery load under dynamic operating conditions for an engine at the typical speed shown in Figure 1. According to the technical data [33], the cut-off voltage is 2.50 V, but after reaching the voltage of 3 V, the capacity change is significantly less noticeable, which further confirms the guidelines of [41]. Figure 16: A system charger (**a**); battery cell current clamp (**b**); and disassembled battery pack cells (**c**). Figure 15: Li-9 on cell charging process and stages of overcharge states [38; 39]. The evaluation of the cells' condition and the parameter measurements showed that the cells' condition in the pack was poor. The best one of all cells had only 48.93% of the initial and nominal capacity. Despite the fact that the resistance values, read by the charger, depend significantly on the cell's electromechanical connection [42], it still can be confirmed that the cells with a higher capacity had the lowest value of internal resistance [43]. The current-voltage (C-V) discharging dynamics of the best cell, cell no. 21, and the cell with the highest capacity, are shown in Figure 17a. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Cell No. **} & **Resistance** & **Capacity** & **Group** & **Remaining** & **Cell** & **Discharge** \\  & **R (mf)** & **C (mAh)** & **Capacity** & **Capacity** & **Voltage** & **Time** \\  & & **C (mAh)** & **(mAh)** & **(mAh)** & **(U V)** & **(min)** \\ \hline
1 & 114 & 351 & 1067 & 15.60 & 3.480 & 13 \\
2 & 101 & 119 & & 5.29  
Finally, discharge-based capacity assessment of all cells within the pack led to a visually representative spatial allocation of cell capacities for both pack assembly layers (TOP and BOT), Figure 18. The results confirm the poor state of the pack assembly and a high level of degradation. In order to confirm cells' capacities determined with the discharging method, a second approach was employed to validate the results. That approach relied on and utilized the charge counting method while the cell was charged up to its maximum voltage but with current that was lower in relation to the nominal discharge current of 2 A--i.e., charge current of 1 A was used. The results of the capacities determined in this way are shown in Table 3.  
Figure 12:0 Comparison of discharge (**a**) and charge (**b**) current–voltage (C-V) characteristics of best performing cell, cell No. 21.