# 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  
To complete the research, further analysis steps were taken to restore the functionality of the battery and make it operational again. The steps that followed included the replacement of the defective, faulty cell with a healthy one. Prior to that, a determination of electrical properties of each cell had to be conducted and correspondingly their spatial arrangement within the pack had to be planned. In this case, a disassembly and the measurement of all 40 battery pack cells was carried out; their state and electrical condition (internal ohmic resistance and charge capacity) were determined using the universal charger JUNS iCharger 1010B+ and terminals with fresh, clean contact surface to achieve the least amount of influence on the contact resistance. It was a difficult and a time-consuming process, but in the interest of the research and the fact that it was a single battery pack, the complete detailed analysis was necessary. In the attempt to revive batteries, which involves the management of larger battery quantities, it is necessary to use methods of cell selection based on the measurement of resistance or X-rays [36]. Prior to  
Figure 11: Overheated healthy cells that conduct the overall battery pack current (a view from different perspectives), (**a**) from rear side and (**b**) from top side. Figure 12: BMS thermal load during charging process at: (**a**) 1:45 PM; (**b**) 1:58 PM; (**c**) 2:05 PM. the analysis continuation, we numerically designated and labeled all battery pack cells for easier analysis management, Figure 13.  
The first two faulty cells, marked with 1 and 3 in Figure 13, do not show voltage within expected, normal operating range. The cells discharged during the measurement despite the high internal resistance of the device. An example of an extreme is cell 1 whose diagram of discharge, via a voltmeter, is shown in Figure 14a. When cell 1 was removed from the cellblock, it mechanically caused a slight perforation of the battery tab weld [37], making it unsafe to handle further. During the cell recharge, cell 3 received voltage values of 5.76 V, which is significantly higher than the maximum allowed values of 4.2 V, Figure 14b. The fact that there was no inflammation clearly indicates the degree of degradation. The behavioral properties, electro-chemical characteristics, and energy transformational mechanisms of battery cells based on Li-ion chemistry are well described and explained in detail in the articles by [PERSON] et al. in _Thermal runaway mechanism of lithium-ion battery for electric vehicles_[38], and by [PERSON] et al. in _Overcharge-induced capacity fading analysis for large format lithium-ion batteries with LiyNi1/3 Co1/3 Mn1/3O2 + LiyMn2O4 composite cathode_[39]. According to the behavioral properties of such battery cells for the measured voltage of 5.76 V, a temperature of more than 50 \({}^{\circ}\)C is expected to be reached, but the cell remained at ambient temperature. That 50 \({}^{\circ}\)C temperature marks a breaking point when the cells start to change their structure mechanically and the deformation of the cell becomes visually noticeable. The absence of the above indicates a significantly impaired capacity of the cell. Figure 15 depicts a charge-thermal dynamic of an overcharged cell in relation to its measured voltage. Figure 14: Cell No. 1 high impedance load discharge graph (**a**) and overcharged cell No. 3, temperature and structurally stable (**b**). Figure 13: Labels of individual cells in the pack arrangement, an assembly (**b**); a top cell layer TOP (**a**); a bottom cell layer BOT (**c**). The measurement setup, shown in Figure 16, consists of a universal Li-ion charger (leftmost), the JUNS iCharger 1010B+, and current clamps (middle image) with a clean contact surface for achieving the lowest possible clamp contact resistance.