Open circuit voltage (OCV) is an important parameter of a battery model. In order to provide accurate state estimation and control command, the battery model parameters have to be calibrated regularly when the battery ages or the model prediction deviates from the data. In this study, an innovative method is developed to reduce the total testing time for taking incremental OCV measurements. In the traditional incremental OCV measurement, the relaxation period is the most time-consuming step waiting until the slow time constant of diffusion dynamics reaches equilibrium. Here, an optimal control problem is formulated to find the minimum-time current profile such that it brings the voltage across the double RC pairs to equilibrium and the initial SOC to target SOC while satisfying the state and input constraints. It is shown by both simulation and experiment that the proposed minimum-time current profile can reduce the total testing time by 69 %.