## 3 LIB SOH Prediction Case Study and Analysis  
### Experimental Data Collection and Preprocessing  
To investigate the variation in capacity and SOH during the charge-discharge process of LIB, we employed 47 DLCG manufactured 18,650 LiFePO4 batteries with a rated capacity of 2500 mAh. Charge-discharge cycle experiments were conducted using a battery tester with the model CT-4008T-5V6A-S1. The specific experimental steps are as shown in Section 2.2, where the battery tester equipment is shown in Figure 3, and the interface for data collection using the BTSDA software is shown in Figure 4. To ensure the applicability of the model, we selected three representative #1, #6, and #26 LIB, from the 47 experimental batteries for SOH analysis. The datasets for these three LIBs consisted of 985, 820, and 656 data points, respectively. Taking the experimental data for #1 LIB as an example, each data point includes 13 types of information, such as cycle index, charge capacity, discharge capacity, and charge-discharge efficiency, among others. A portion of the original data is presented in Table 1.  
Figure 3: Battery tester equipment. The original data do not meet the conditions for direct analysis, and require processing to transform them into standardized data. Firstly, any instances of missing values and outliers in the original charge-discharge cycle experimental data are removed. Secondly, the 3 Sigma method is used to analyze whether there are abnormal data in the data. If there are, they will be processed. For example, in the data of the 204 th cycle in the original data in Table 1, there are anomalies in all the other data except for the consistent-charge-capacity and charge-time data. The average value of the data of the same category as the abnormal data in the last cycle and the next cycle is taken as the processed data, as shown in Table 2. Lastly, the Min-Max standardization method is applied to the data to standardize feature variables' dimensions and scales. This standardization approach helps mitigate discrepancies in dimensions, which can lead to interpretation biases. It imparts greater interpretational significance to the model results, and enhances model precision. In addition, the number of data after processing has not changed; there are still 985 pieces of data, and some of the processed data are shown in Table 3.  
The battery data obtained from the aforementioned #1 LIB charge-discharge cycle experiment yield a discharge capacity trend, as shown in Figure 5. Through this graph, it can be observed that, with an increase in the number of charge-discharge cycles, the overall discharge capacity of the LIB gradually decreases. However, there are also instances of partial capacity recovery, which is a normal occurrence. The SOH of the LIB is defined as the ratio of discharge capacity to rated capacity under specific charge-discharge conditions. As the discharge capacity gradually decreases, SOH also decreases. When SOH falls below 80%, the battery's range, charge-discharge efficiency, and other performance metrics start to deteriorate. This deterioration can potentially impact the normal operation of new-energy electric vehicles, posing a risk to road traffic safety. Therefore, it is essential to carry out early prediction of LIB SOH. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Cyde Index**} & \multirow{2}{*}{ \begin{tabular}{c} **Charge** \\ **Capacity (Ah)** \\ \end{tabular}  } & \multirow{2}{*}{ \begin{tabular}{c} **Discharge** \\ **Capacity (Ah)** \\ \end{tabular}  } & \multirow{2}{*}{ \begin{tabular}{c} **Constant Current** \\ **Discharge** \\ **Efficiency (\%)** \\ \end{tabular}  } & \multirow{2}{*}{ \begin{tabular}{c} **Constant Current** \\ **Charging** \\ **Ratio (\%)** \\ \end{tabular}  } & \multirow{2}{*}{ \begin{tabular}{c} **Mean** \\ **Charging** \\ **Capacity (Ah)** \\ \end{tabular}  } & \multirow{2}{*}{\ \begin{tabular}{c} **Change** \\ **Voltage (V)** \\ \end{tabular}  } & \multirow{2}{*}{ \begin{tabular}{c} **Discharge** \\ **Time** \\ \end{tabular}