Electric Vehicle (EV) dynamic charging is a new charging technology that has received attention recently from both industry and academia. It is much convenient compared to plug-in power charging. However, the EVs need to pay and authenticate to charging pads placed on roads to get charged. because of its wireless and fast moving nature, dynamically offering services (including secure and reliable payment based access, power charging, etc.) to the paid users is challenging. In an efficient physical-layer-based authentication scheme, the EVs should sent digital secret token to the pads that should verify them. To design a scheme that meets both security and reliability requirements in EV dynamic charging scenario, this paper analyzes and evaluates the verification performance. Probabilistic performance metrics are defined and an analytic framework is developed to quantify the performance. The derived estimation formulas are validated by numerical results, and these results reveal the sensitive impacts of token-pool Hamming distance, decision threshold and Signal-to-Noise Ratio (SNR).