A system for reversibly storing electrical energy as thermal energy. The system can include a reversible subcritical vapor-liquid cycle energy storage system with a single hot storage fluid tank and cold storage fluid tank that are inter connected by an inter storage tank flow path. The inter storage tank flow path includes an inter storage heat exchanger in the vapor-liquid cycle that enables sensible heat transfer between the working fluid and storage fluid as the storage fluid passes between the hot storage fluid tank and the cold storage fluid tank. This supplements latent heat transfer between the working fluid and the hot storage fluid tank and the cold storage fluid tank.