The article presents a new method called EKF-Ah for accurately estimating the state of charge (SOC) of lithium-ion power batteries in electric vehicles. This method combines the extended Kalman filtering algorithm with ampere hour counting to improve SOC estimation in complex environments. Laboratory tests showed that the EKF-Ah method has a maximum SOC estimation error of under 6.5%, demonstrating its effectiveness in accurately estimating the SOC of power batteries.