The new battery plant could produce more batteries in one year than the industry made last year. (Reuters)

So it’s a great car. Is it a great stock?

Shares of Tesla Motors shot up 17 percent Tuesday morning, putting the value of the company at more than $31 billion – and that was before Consumer Reports announced that Tesla’s Model S was the best overall car of the year.

Tesla rose after Morgan Stanley analysts raised their price target for Tesla to $320 a share. At 11:30 a.m., Tesla had jumped to $254.63 a share, up $36.98. The stock was already up since its quarterly earnings on Feb. 19 because of anticipation about the company’s plans for a “gigafactory” that would make battery packs.

The Consumer Reports review can only make jubilant shareholders happier: “Sure, you can talk about this electric luxury car’s blistering acceleration, razor-sharp handling, compliant ride, and versatile cabin, which can fit a small third-row seat. But that just scratches the surface of this technological tour de force. The Tesla is brimming with innovation.” Consumer Reports bases its assessment on performance, reliability and safety.

But is it a great stock? A lot of investors have been asking that question for the past year and during that time the stock is up 644 percent. A lot of investors are still asking that question. Pessimists about Tesla have shorted 29.6 million shares, or 37.31 percent of the outstanding shares not owned by insiders. That means those investors expect the price to drop and they hope to buy shares later at lower prices to cover the shares they have borrowed to sell now at a high price.

The value of Tesla’s shares, its market capitalization, is now more than half the value of General Motors or Ford Motor. Optimists about Tesla say the company is the Apple of the auto business, destined to define style, safety and performance while posting big profit margins and new products, including new batteries. Skeptics look at Tesla and say it’s the latest bubble stock.

Of the Consumer Reports 10 best cars of the year, none belonged to either of the big two. Indeed U.S. carmakers fared poorly all around. Consumer Reports named the Honda Accord best midsized sedan, the Toyota Prius the best green car, Subaru Forester as best small SUV, Subaru Impreza as best compact, the Audi A6 as best luxury car, the BMW 329i as best sports sedan, Hyundai Santa Fe as best mid-sized SUV, and the Honda Odyssey as best minivan. The Dodge Ram 1500 was the best pickup truck.

But consider the comparison to GM. Sure, GM and Ford have a lot of baggage. But in January alone GM sold 171,486 vehicles in the United States alone. Tesla’s optimistic forecast for this entire year is that it will sell 35,000 vehicles worldwide. In 2013, Tesla sold 22,477 cars, while GM sold 2.8 million in the United States and 9.7 million worldwide.

 Tesla’s sales are a rounding error for GM or Ford.

What’s more, GM and Ford are now profitable, making billions of dollars each last year. Tesla is still losing money, albeit less and less every quarter. It’s a big gap. Can Tesla close it? And when?