The Elon partner you are referring to is Kiwi Ian Wright of Wrightspeed . He raised $400M in venture capital and is making EREV powertrain replacements for garbage trucks. He was on one of the American business cable news channels last week saying Tesla's pure EV Semi truck is impossible, that it needs a fossil fuel range extender.
He has repeatedly said Elon's plan to make an every cheaper BEV in ever greater numbers to eventually compete head on with Toyota and the Camry is impossible.