We report high performance composite solid polymer electrolytes for electrochemical cells with comprehensive properties in high mechanical strength and high ionic conductivity. The composite electrolytes consist of porous non-woven polymer filament substrates that are impregnated with high ion-conducting materials. To insure structural integrity, the non-woven polypropylene/polyethylene core–shell substrates are sulfonated to activate the surface. The high ion-conducting materials are prepared from poly(vinyl alcohol) with the incorporation of acrylic acid monomer and cross-linking agent. The results show well-balanced physical and electrochemical characteristics that warrant excellent battery discharge capacity and cell power density. The room temperature ionic conductivity is high at 0.16–0.21 S cm−1, and the activation energy is low at 0.5 kJ mol−1. The mechanical strength is improved to 12 MPa with good elongation at 58–62%. The anionic transport numbers (t −) are in the range of 0.93–0.99 in 1 M KOH, 0.91–0.97 in 1 M NaOH, and 0.83–0.91 in 1 M LiOH, respectively. The cyclic voltammetric study indicates good stability with symmetric curves between the cathodic and anodic peaks. The fully solid-state metal–air fuel cells exhibit excellent discharge capacity of 1506 mAh and high anode utilization of 95.7%. The power density is achieved at 91 mW cm−2.