(Adds details from the release, background) April 19 (Reuters) - SES said on Monday it had raised $139 million in a funding round led by General Motors, as the lithium metal battery startup benefits from rising demand for electric vehicles. GM last month announced a partnership with SES to boost its battery development, allowing for higher electric vehicle driving range in a smaller package - a key goal for automakers as they push to roll out electric vehicles. (reut.rs/2P3UDn6) “GM has been rapidly driving down battery cell costs and improving energy density, and our work with SES technology has incredible potential to deliver even better EV performance for customers who want more range at a lower cost,” GM executive vice president Matt Tsien said in a statement. The companies plan to build a manufacturing line in Woburn, Massachusetts to assemble a prototype battery by 2023. GM in 2015 invested an undisclosed amount in SES. The startup said on Monday that its latest funding round also included existing investors SK Inc, Singapore state fund Temasek, Applied Ventures LLC, Shanghai Auto and Vertex. (Reporting by Shreyasee Raj; Editing by Aditya Soni)