## 3 Experiments and Data Processing  
### Battery Testing Platform  
The test object of this work is a SONY lithium-ion battery called US18650 VTC5. Its nominal capacity and nominal voltage are 2.5 Ah and 3.6 V, respectively. In order to create \begin{table}
\begin{tabular}{c c c} \hline \hline
**Layer** & **Each of Layer** & **Number of Neurons** \\ \hline GRU & GRU\_1 & 200 \\ GRU & GRU\_2 & 214 \\ GRU\_3 & 152 \\ FCL & FCL & 106 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Optimized of parameters of GA-GRU model. Figure 3: The implementation process of GA-GRU model. a dataset to validate the proposed algorithm, we established a battery testing platform as shown in Figure 4. It mainly consists of four parts: a host computer, battery test equipment, a temperature chamber, and batteries. The host computer is used to control the battery test equipment and collect the battery data. The battery test equipment is responsible for charging or discharging batteries under different conditions and sending battery data to the host computer. The temperature chamber is utilized to control the ambient temperature for batteries. The hardware configurations of the battery testing platform are shown in Table 2.  
The test process of batteries includes the charging process and the discharging process. In order to fully charge batteries, we adopted the method of constant current charging (CC) and then constant voltage charging (CV). During the constant current charging phase, a current of 2.5 A was applied to the battery until the battery voltage reached 4.2 V. Then, when we entered the constant voltage charging phase, the battery maintains 4.2 V voltage and continues to charge until the battery current was less than 0.05 A. In order to simulate the driving conditions of electric vehicles as realistically as possible, we employed four dynamic driving cycles in the discharging process. At the same time, five temperatures (0 \({}^{\circ}\)C, 10 \({}^{\circ}\)C, 20 \({}^{\circ}\)C, 30 \({}^{\circ}\)C, and 45 \({}^{\circ}\)C) were used to simulate the low temperature, normal temperature, and high temperature in real life. These four dynamic driving cycles were the Beijing Dynamic Stress Test (BJDST), the Federal Urban Driving Schedule (FUDS), the Dynamic Stress Test (DST), and the US06 Highway Drive Schedule (US06) [29; 30; 31]. The durations of each condition for one cycle were 900 s, 1372 s, 360 s, and 596 s, respectively. In \begin{table}
\begin{tabular}{l l l} \hline
**Hardware** & **Specification** & \\ \hline \multirow{3}{*}{TECHPOW battery test equipment} & Voltage range & 0–5 V \\  & Current range & \(-\)200 A-200 A \\  & Sampling precision & 0.001 \\  & Temperature range & \(-\)40 \({}^{\circ}\)C\(\rightarrow\)+150 \({}^{\circ}\)C \\  & Sampling precision & 0.1 \({}^{\circ}\)C \\ \hline \end{tabular}
\end{table} 
Table 2: The battery testing platform specification. Figure 4: Battery testing platform. this paper, four identical batteries were used for testing. The test conditions for each of the four batteries were as follows: (1) the first battery was tested under BJDST at five different temperatures (0 \({}^{\circ}\)C, 10 \({}^{\circ}\)C, 20 \({}^{\circ}\)C, 30 \({}^{\circ}\)C, and 45 \({}^{\circ}\)C); (2) the second battery was tested under FUDS at five different temperatures (0 \({}^{\circ}\)C, 10 \({}^{\circ}\)C, 20 \({}^{\circ}\)C, 30 \({}^{\circ}\)C, and 45 \({}^{\circ}\)C); (3) the third battery was tested under DST at five different temperatures (0 \({}^{\circ}\)C, 10 \({}^{\circ}\)C, 20 \({}^{\circ}\)C, 30 \({}^{\circ}\)C, and 45 \({}^{\circ}\)C); (4) the fourth battery was tested under US06 at five different temperatures (0 \({}^{\circ}\)C, 10 \({}^{\circ}\)C, 20 \({}^{\circ}\)C, 30 \({}^{\circ}\)C, and 45 \({}^{\circ}\)C). The battery data collected under US06 at 20 \({}^{\circ}\)C is shown in Figure 5. Finally, a total of 20 data subsets and 180,000 samples were obtained through these experiments.