DETROIT, May 29 (Reuters) - A battery plant partly owned by General Motors GM.N is delaying the return of hundreds of workers in northeast Ohio amid continued weak demand for electric cars, according to sources and an internal announcement sent to employees and viewed by Reuters.

Workers at the Ultium Cells plant in Warren, Ohio, jointly owned by GM and LG Energy Solution, are now being told they will begin to return to work in August, the sources and document said. They have been out of work since January, when they were given a June return-to-work timeframe.

Ultium Cells did not immediately respond to a request for comment.