Given the following parameters of an EV battery: battery capacity E = 150kWh, the final state of charge (SOC) SOC₁ =70%, charging power P_ch = 60kW, discharging power P_dis = 30kW, charging time t_ch = 1 hours, discharging time t_dis = 1.8 hours, charging efficiency η_ch = 90%, and discharging efficiency η_dis = 90%, what is the initial SOC (SOC₀) of the battery? (The related formulas are as follows)