Not long after the auto bailouts, the financial crash and the election of President Obama, General Motors Co. had a choice to make. It had designed an electric car, the Chevrolet Volt, to prove it could build something besides gas guzzlers. To make this car even close to affordable, it would need a battery unlike any that had been made before. To discover that battery, GM had been working with two companies, one Korean and one American. And the time had come to choose.