A123 Systems Inc., the Waltham battery maker, said Sunday that it plans to sell nearly all its assets to the North American arm of China’s largest auto parts manufacturer for $256.6 million, pending approval by US Bankruptcy Court and the federal government.

What effect the new ownership, by Wanxiang America Corp., would have on A123’s business and jobs in Michigan and Massachusetts is unclear, but Wanxiang has said it is committed to keeping and expanding the company’s US operations. A123 has about 1,000 US employees, including roughly 300 in ­Massachusetts.