SAN FRANCISCO (MarketWatch) -- Tesla Motors Inc. TSLA, +4.42% and Japan's Panasonic Corp. 6752, -0.50% have reached a deal for Panasonic to invest in Tesla's 'gigafactory,' according to reports Monday citing Japan's Nikkei. Panasonic would invest about $200 million to $300 million in the factory, and an official announcement is expected by the end of the month. Shares of the electric car maker rose 2.5% on the news. Panasonic had signed a letter of intent to join the battery factory in May, but doubts had swirled as the Japanese electronics maker is in the midst of a restructuring. Panasonic is the main supplier of battery cells for Tesla. Tesla has said it is evaluating sites in Arizona, California, Nevada, New Mexico, and Texas to place its massive battery factory, which could cost as much as $5 billion. The electric car maker would break ground on the 'gigafactory' later this year, and the factory is expected to reach full capacity by 2020, providing battery packs to about 500,000 cars a year.