This paper presents a novel method for the estimation of the lead-acid battery initial state of charge (SOC) using the battery impedance measurement. The initial SOC is a crucial value used in the commonly used Coulomb counter. An experimental test bench for battery characterization and impedance measurement is built using CompactRio and Labview software. A very simple electrical circuit is proposed and designed allowing the determination of the initial SOc. Mathematical formulas are derived allowing obtaining a good estimation of the initial SOc. The simulation results are validated experimentally.