The increasing penetration of wind-based renewable energy introduces significant challenges to voltage stability and transmission system security due to the intermittent nature of wind generation. This study proposes a Discrete Grey Wolf Optimization (DGWO)-based framework for the optimal placement and sizing of Battery Energy Storage Systems (BESS) in the 150 kV South Sulawesi transmission system under high renewable-energy penetration conditions. The investigated network integrates large-scale wind generation from the Sidrap (275 MW) and Jeneponto (260 MW) wind farms. The proposed framework combines inverter-constrained BESS operation, adaptive reactive power control, wind curtailment management, and AC power flow analysis within a unified multi-objective optimization structure. The optimization identifies optimal BESS installations at Buses 1, 19, and 25 with reactive power capacities of 5.37 MVAr, 7.60 MVAr, and 39.19 MVAr, respectively. Simulation results under the worst-case operating condition demonstrate that the proposed approach improves the minimum bus voltage from 0.9400 pu to 0.9590 pu while maintaining all transmission line loadings within the thermal security limit of 250 MVA. The optimized solution requires only 15.51 MVAr of actual reactive power utilization and limits wind curtailment to 0.98%. In addition, most fitness improvement is achieved before iteration 60, indicating stable convergence and good computational efficiency. The results confirm that the proposed approach provides an efficient, technically feasible, and operationally realistic solution for voltage stability enhancement and secure operation of renewable-integrated transmission systems.