WILMINGTON, Del. — A bankruptcy judge on Tuesday approved the sale of most assets of the failed Massachusetts battery maker A123 Systems Inc. to the US arm of a Chinese auto parts conglomerate, Wanxiang Group, for nearly $257 million.

In asking Judge Kevin Carey to approve the sale, attorneys for A123 noted that the winning bid, submitted by Wanxiang America Corp. last week, was more than double an initial $125 million offer for the company’s automotive battery unit by the Milwaukee auto parts marker Johnson Controls Inc.