MEXICO CITY, Sept 12 (Reuters) - Spanish battery maker Endurance Motive will start production in the central Mexican state of Puebla next year, becoming one of the first firms to assemble lithium batteries for vehicles in the country, an executive said on Tuesday.

Endurance assembles lithium iron phosphate batteries for use in boats, last-mile delivery vehicles and industrial equipment such as forklifts and small tractors.

The company plans to begin production in March 2024 for the Mexico market, with the goal of reaching U.S. clients in the coming years, said Francisco Molla, Endurance's Mexico director, in an interview.

He declined to say how much was being invested by Endurance, which he said was founded six years ago and is still small.

Mexico has attracted more investment in the electric mobility sector as automakers shift away from gas-powered vehicles, but battery makers have yet to gain a foothold.

Molla said the substantial investment and technical expertise needed for battery assembly had created high barriers for companies to begin producing in Mexico. However, growing demand was beginning to justify the high costs.

"I'm not going to say it's mainstream, but now it's taking off, there's no going back," he said.

The company chose Puebla for its central location, and will open near a large Volkswagen complex and various auto industry suppliers, Molla said.

Endurance's batteries in Mexico will initially contain about 30% to 35% domestic components with lithium cells imported from China. Molla said the company aims in a couple of years to boost local content to more than 50%. (Reporting by Daina Beth Solomon; Editing by Jamie Freed)