FUJI, Japan — At a factory near the base of Mount Fuji, workers painstakingly assemble transmissions for some of the world’s top-selling cars. The expensive, complex components, and the workers’ jobs, could be obsolete in a couple of decades.

The threat: battery-powered electric vehicles.

Their designs do away with the belts and gears of a transmission, as well as thousands of other parts used in conventional cars. Established suppliers are nervous, especially in Japan, where automaking is a pillar of the economy — and where industrial giants have been previously left behind by technological change.

“If the world went all-E.V. today, it would kill my business,” said Terry Nakatsuka, chief executive of Jatco, the company that owns the transmission factory, using a shorthand term for electric vehicles.

With 7,000 workers, Jatco is part of a vast ecosystem of carmakers and suppliers that provides one in 10 Japanese jobs, accounts for a fifth of national exports and generates more profit than any other industry in Japan.