Investigations were conducted to study the feasibility of a solid-state battery system for storage applications. During the development of various high energy density solid-state batteries we noted that the solid electrolyte material, LiI dispersed in large surface area Al2O3, has a high ionic conductivity at elevated temperatures, (for example 0.1Ω−1 cm−1 at 300° C) and is suitable for high-rate storage battery applications. In solid-state battery systems both the electrodes and electrolytes are in the solid state under the operating conditions of the battery. The absence of any liquid phase makes the individual cell containers unnecessary in a multicell battery resulting in a simplified battery structure and increased package efficiency. Furthermore, no material compatibility problem is encountered in the system. As a result, the solid-state battery system has excellent charge retention characteristics and a long projected operating life. Solid-state test cells, Li-Si/LiI(Al2O3)/TaS2/Ta, Li-Si/LiI(Al2O3/TiS2/Ti and Li-Si/LiI(Al2O3)/TiS2, Sb2S3, Bi were constructed and subjected to discharge-charge cycle tests at 300±10° C, at 13·7 mA cm−2. Preliminary test results demonstrated that these solid-state battery systems are rechargeable and may be suitable for both load levelling and/or vehicle propulsion. From the considerations of material availability and cost and operational efficiencies it was concluded that the Li-Si/LiI(Al2O3)/TiS2, Sb2S3, Bi system is most suitable among the three systems studied for the development of practical storage batteries. Preliminary design studies showed that practical energy densities of 200W h kg−1 and 520 W h l−1 can be realized with the Li-Si/TiS2, Sb2S3, Bi storage batteries.