Can Tesla really deliver on its promise to offer a long-range electric vehicle that is cheap enough to attract mainstream buyers by 2017? We can’t know for sure without access to the company’s proprietary information. But one thing is clear: if Tesla is successful it will be because of significant advances to the design and manufacturing of its battery pack, which many estimates suggest represents a quarter to half of the full cost of the car.

At a launch event Thursday night in Los Angeles, Elon Musk announced that the Tesla Model 3 would have a range of 215 miles. That’s not much less than the range of the cheapest version of the older Model S sedan. But the Model S starts at nearly $70,000—twice the Model 3's $35,000 price tag.

Where might the cost savings come from? Some may come as Tesla learns to improve how efficiently it builds batteries at its "gigafactory," which is now under construction in Nevada.

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