With the continuous growth of new energy vehicle ownership, power batteries have massively entered the in-use phase. However, issues related to their performance degradation and safety risks are becoming increasingly prominent in actual operation and testing work. During long-term service, characteristics of power batteries such as capacity decline, increased internal resistance, and deterioration of consistency not only affect usage performance but also directly impact thermal stability and safety boundaries. Nevertheless, current power battery maintenance and management practices still primarily use capacity degradation as the main retirement criterion. This single indicator has limitations in accurately reflecting the actual safety status of batteries. Based on practical needs for testing and evaluation of in-use power batteries, this paper analyzes key factors affecting the safety performance of in-use power batteries from an application perspective, incorporating battery aging mechanisms and typical safety failure modes. Building on this analysis, it proposes a dual-dimensional comprehensive testing and evaluation framework covering both electrical performance and safety performance. The relevant research can provide reference for improving safety management of in-use power batteries and refining technical specifications for retirement determination.