HONG KONG  The investor Warren E. Buffett announced on Monday that he had agreed to buy a 9.89 percent stake in a Chinese battery manufacturer that plans to sell electric cars in the United States by 2010.

The MidAmerican Energy Holdings Company, will pay 1.8 billion Hong Kong dollars  about $230 million  for the stake in the battery maker, the BYD Company. Mr. Buffett’s Berkshire Hathaway owns 87.4 percent of MidAmerican.

Based in Shenzhen, a mainland Chinese city adjacent to Hong Kong, BYD is one of the world’s largest makers of rechargeable batteries for cellphones and other uses. The company also has a fast-growing auto-making unit that accounts for nearly a third of its revenue and makes fuel-efficient compact and subcompact cars for the Chinese market.

The president of BYD, Wang Chuanfu, said that the alliance with Mr. Buffett was not just about raising capital for the manufacturer, which relies heavily on short-term debt.