Four years ago, the BYD Company promoted the electric battery technology it was developing as a way to help China transform the automobile. No less an investor than Warren E. Buffett, one of the world’s richest men, boasted about the company’s prospects and bought a 10 percent stake.

But recently, nothing has gone right. BYD's stock is down 43 percent from its high on Feb. 8 as investors and analysts have questioned whether the company has the technology or the manufacturing quality to be an enduring competitor in the Chinese market.