## 3 Effects of Storage and Maintenance Modes on Battery Performance
### Effects of Storage SOC on Battery Performance
#### 3.5.2 Effects of Storage SOC on Battery Power  
The \"storage SOC\" refers to the SOC value with which the Ni-MH battery modules are stored. For example, 30% storage SOC means that the SOC value is 30% when the battery modules were initially stored. On the other hand, the \"present SOC\" refers to the SOC values reached during the discharge process of the performance test before or after storage, including 80%, 50%, and 20%.  
With a present SOC of 80%, 50%, and 20%, the effects of different storage SOC on battery charge-discharge power were evaluated. The test results are shown in Table 9. The 30% storage SOC clearly presented itself as the best approach to maintain the power of Ni-MH battery modules.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**SOC Value** & **Manufacturer** & \begin{tabular}{c} **Method** \\ **Number** \\ \end{tabular} & \begin{tabular}{c} **Storage** \\ **SOC** \\ \end{tabular} & \
\begin{tabular}{c} **Change Rate of** \\ **Charge Power** \\ \end{tabular} &
\begin{tabular}{c} **Change Rate of** \\ **Discharge Power** \\ \end{tabular} \\ \hline \multirow{3}{*}{80\% SOC} & A & 1 & 50\% SOC & \(-\)19.4\% & \(-\)18.1\% \\  & & 2 & 30\% SOC & \(-\)12.6\% & \(-\)12.2\% \\  & B & 1 & 50\% SOC & \(-\)17.4\% & \(-\)26.8\% \\  & B & 2 & 30\% SOC & \(-\)11.1\% & \(-\)23.0\% \\ \hline \multirow{3}{*}{50\% SOC} & A & 1 & 50\% SOC & \(-\)21.4\% & \(-\)18.9\% \\  & A & 2 & 30\% SOC & \(-\)11.3\% & \(-\)10.3\% \\  & B & 1 & 50\% SOC & \(-\)23.4\% & \(-\)26.7\% \\  & B & 2 & 30\% SOC & \(-\)21.6\% & \(-\)23.1\% \\ \hline \multirow{3}{*}{20\% SOC} & A & 1 & 50\% SOC & \(-\)19.8\% & \(-\)28.3\% \\  & & 2 & 30\% SOC & \(-\)11.1\% & \(-\)21.1\% \\ \cline{1-1}  & B & 1 & 50\% SOC & \(-\)23.8\% & \(-\)26.1\% \\ \hline \hline \end{tabular}
\end{table}
Table 9: Effects of different storage SOC on power change rate of Ni-MH battery modules with different SOC.  
Figure 19: Effects of different charge rates on efficiency change rate of Ni-MH battery modules: (**a**) change rate of charge efficiency; (**b**) change rate of discharge efficiency.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**SOC Value** & **Manufacturer** & \begin{tabular}{c} **Method** \\ **Number** \\ \end{tabular} & \begin{tabular}{c} **Storage** \\ **SOC** \\ \end{tabular} & \
\begin{tabular}{c} **Change Rate of** \\ **Charge Power** \\ \end{tabular} &
\begin{tabular}{c} **Change Rate of** \\ **Discharge Power** \\ \end{tabular} \\ \hline \multirow{3}{*}{80\% SOC} & A & 1 & 50\% SOC & \(-\)19.4\% & \(-\)18.1\% \\  & A & 2 & 30\% SOC & \(-\)12.6\% & \(-\)12.2\% \\  & B & 1 & 50\% SOC & \(-\)17.4\% & \(-\)26.8\% \\  & B & 2 & 30\% SOC & \(-\)11.1\% & \(-\)23.0\% \\ \hline \multirow{3}{*}{50\% SOC} & A & 1 & 50\% SOC & \(-\)21.4\% & \(-\)18.9\% \\  & A & 2 & 30\% SOC & \(-\)11.3\% & \(-\)10.3\% \\ \cline{1-1}  & B & 1 & 50\% SOC & \(-\)23.4\% & \(-\)26.7\% \\ \cline{1-1}  & B & 2 & 30\% SOC & \(-\)21.6\% & \(-\)23.1\% \\ \hline \multirow{3}{*}{20\% SOC} & A & 1 & 50\% SOC & \(-\)19.8\% & \(-\)28.3\% \\ \cline{1-1}  & A & 2 & 30\% SOC & \(-\)11.1\% & \(-\)21.1\% \\ \cline{1-1}  & B & 1 & 50\% SOC & \(-\)23.8\% & \(-\)26.1\% \\ \cline{1-1} \cline{1-1}  & B & 2 & 30\% SOC & \(-\)23.0\% & \(-\)12.0\% \\ \hline \hline \end{tabular}
\end{table}
Table 8: Effects of different storage SOC on capacity of Ni-MH battery modules.