# Application of Infrared Thermography in E-Bike Battery Pack Detail Analysis--Case Study
## 5 Conclusions  
Infrared thermography is a practical and non-destructive test and measurement method for battery condition assessment and analysis, but only in a qualitative way. Changes in a battery and battery cells' temperature values, due to thermal capacity and thermal resistance, can only provide information on the battery condition. On the thermograms of healthy batteries, a temperature difference of 2.1 \({}^{\circ}\)C was found at points with \begin{table}
\begin{tabular}{c c c c c c c c c c c}  & & & & \multicolumn{3}{c}{**10s**} \\ \hline \hline \multirow{3}{*}{\(\Delta\) to avg.(mAh) \%} & 2117 & 2326 & 2255 & 2283 & 2412 & 2128 & 2381 & 2696 & 2412 & 1455 \\  & 1318 & 951 & 1009 & 953 & 820 & 1094 & 840 & 387 & 566 & 1328 \\ \hline \multirow{2}{*}{\(\Delta\) to avg.(mAh) \%} & **3435** & **3277** & **3264** & **3236** & **3232** & **3222** & **3221** & **3083** & **2978** & **2783** \\  & & & & & & & & & & & \\ \end{tabular}
\end{table} 
Table 6: Optimal layout of pack compound in 2p10s configuration restated from the used cells (considering its capacities, mAh). Figure 23: Repaired and revived battery pack: an assembly (**a**) and its thermal footprint (**b**). similar cells. At the end of the battery life, this difference was slightly larger and amounted to 2.4 \({}^{\circ}\)C. The reported values were close to the camera accuracy of \(\pm\)2 \({}^{\circ}\)C and depended on power dissipation due to current that we could not measure. Therefore, general conclusions based on absolute temperature values are not possible. Owing to the high thermal sensitivity of the NETD camera, the pattern can be seen. The faulty battery had the largest temperature difference of 5.5 \({}^{\circ}\)C, which, according to a recommendation from the literature, is an indication of a possible defect (needs to be investigated). The homogeneity of the thermal pattern can serve as a criterion for assessing the health and service expectancy of the battery pack. Thermal hotspots within a pack, which occur when one or more battery cells start to fail, are caused by overloading of healthy cells. Contrary to the common reasoning, where hotspots represent a place of failing component, the situation here is the opposite. The hotspot represents a place of a normal operational component that generates excessive heat due to acting as a charging current sink, having low resistance within a cell-block. In addition, the thermographic analysis of the balancing circuitry can also provide information about the state of charge and capacity of individual cells by monitoring the power dissipation at each balancing resistor over time. Due to the way the e-bike's battery pack operates, a failure of the battery pack usually inevitably means a failure of all the cells. The main factors leading to the battery cell failure are cell aging and operating conditions associated with high operating and resting temperatures. In order to draw conclusions based on thermographic records, detailed knowledge of the physical behavior of the object under study is required. Therefore, it was necessary to perform a detailed analysis of the battery pack. The main conclusion of the study is that it is not possible to make a judgment about the appearance of the thermal pattern or the pattern shape based on the estimated capacity values. However, based on the thermal pattern, it is possible to make a judgment about the homogeneity of the capacity of individual battery cells. Thus, in its qualitative form, infrared thermography is an ideal non-destructive method for monitoring the condition of e-bike batteries. Due to the high thermal sensitivity/NETD of today's thermal imaging cameras, the dynamic of thermal pattern during charging and discharging can provide information about the condition of a battery pack. Conceptualization, H.G. and M.K. ; methodology, H.G. and T.B. ; software, M.K. and T.K. ; validation, T.K. and T.B. ; formal analysis, H.G. ; investigation, H.G. ; resources, H.G. and M.K. ; data curation, H.G., T.B., T.K. and M.K.