“We need more cells” was Elon Musk’s mantra in Tesla’s Q3 earnings call this week, as he highlighted the challenges that the company currently faces in scaling the manufacturing of its Tesla Semi truck. As electric offerings start to pop up in larger and larger vehicles, the role of hydrogen fuel cells in the transport market could hinge on Tesla’s success in supplying low-cost batteries. The “cell constraint” that Musk stated was “the only real constraint on the Semi’s progress,” refers to the fact that as vehicles get larger, they need more power. For battery electric vehicles, this means adding more cells, which in turn adds more cost to and already profitability-challenged vehicle. This is an ‘energy density problem,’ and…