U.S. electric vehicle maker Tesla will increase its investment in battery cell production at its plant outside Berlin by almost $250 million, boosting its capacity target for the site, the company said on Tuesday. Tesla announced in December investments amounting to almost 1 billion euros ($1.2 billion) at the site in Gruenheide, south-east of the German capital, as it seeks to bring battery cell and vehicle production all under one roof from next year. With the latest investment, Tesla plans to create the conditions for annual production capacity of 18 gigawatt hours, up from a previously planned 8 GWh.