In view of the high safety requirements of the power system, the valve-regulated lead-acid (VRLA) batteries used in substations still have considerable secondary utilization value after retirement. The estimation of the state of health (SOH) for retired VRLA batteries is influenced by various factors, among which the state of charge (SOC) has the most significant impact and is difficult to determine when the battery capacity is unknown. This paper presents an experimental study on retired batteries under unknown SOC, using a preprocessing state for the batteries to reduce the time required to determine their condition. By analyzing and extracting features from electrochemical impedance spectroscopy (EIS), hybrid pulse power characterization (HPPC), and different current discharge experiments, multiple health characteristic parameters applicable to the estimation of SOH for retired batteries were identified. The proposed preprocessing of retired battery states, along with the prediction of SOH using multiple health characteristics, not only significantly reduces the time needed to determine SOH compared to the traditional ampere-hour integration method, thus improving efficiency, but also achieves a comprehensive estimation of SOH through multiple health characteristics, enhancing the accuracy of the SOH estimation.