In 2020, QuantumScape (QS -2.08%) was one of the hot stocks to hold, according to Wall Street. The stock back rose as high as $115 per share with a market cap approaching$50 billion. Investors then swooned over the company's potential to revolutionize electric vehicle charging through solid-state lithium-metal battery technology.After a steep decline starting in 2021, shares now trade at just $4, with the company having a market cap of around$2.2 billion. Some investors now wonder if it's time to buy this ...