<p>The increasing reliance on renewable energy for grid-connected and off-grid applications has led to a greater interest in reducing their costs. This paper presents a novel attempt for optimizing off-grid wind-battery systems. The turbine geometrical parameters—turbine diameter, tip-speed-ratio, airfoil type, and chord and twist distributions—are incorporated into the optimization along with battery capacity. A complete mathematical model was developed incorporating the blade element momentum theory to analyze the wind turbine, the Weibull distribution to evaluate the wind regime, and a battery model. The differential evolution algorithm was utilized to obtain the optimal system design for a realistic case in Egypt, resulting in a system achieving a 100% demand fulfillment with a levelized cost of energy of 0.536 $/kWh. Results revealed that the design tip-speed-ratio ranged from 5 to 7, with the E387 and SG6043 airfoils deemed most suitable for the given wind regime. The chord length and twist distributions were increased near the blade root to enhance turbine starting performance, and the battery cost accounted for 84.17% to 96.26% of the energy cost. Sensitivity analysis was conducted to evaluate the robustness of the proposed system by analyzing the effects of changing the battery cost, turbine cost, turbine diameter, interest rate, and wind regime statistics on optimization results. It was found that reducing the battery cost and increasing the turbine diameter could save up to 40.1% of the energy cost. The proposed methodology has proven its effectiveness in optimizing the design of off-grid wind-battery systems in any location.</p>