Japan-based NGK Insulators has transformed an experimental battery-which Ford Motor pursued for use in electric cars for more than 30 years-into a technology that could help manage the production of electric power. Each cell in the sodium and sulfur battery produces two volts when positively charged sodium ions pass through a ceramic tube and combine with negatively charged sulfur. Earlier versions of the technology could provide about 50 kilowatts, enough to supplement an office building’s power supply during peak hours. By improving the ceramic’s purity, NGK was able to reduce its thickness by 25 percent, to 1.3 millimeters. That in turn lowered its electrical resistance. The reduced resistance, combined with an altered design, allows the new battery to switch on in less than a millisecond and deliver 250 kilowatts, enough to supply backup juice during temporary power failures. This summer, NGK brought one of the new batteries on line for U.S. utility provider American Electric Power at one of its plants in Ohio.