Stealthy battery company backed by Bill Gates, Jeff Bezos has a lot to prove

 

On Tuesday, Form Energy announced it closed a $240 million Series D funding round. Among the backers renewing is Breakthrough Energy Ventures, which includes celebrity investors like Bill Gates and Jeff Bezos.

The company has not shared data or proof its iron-air battery technology works with the public.

CNBC talked to investors, partners and outside experts to get their take on the viability and looming questions about Form Energy’s technology.