The Chevy Volt is unique among electric cars because it runs on two sources of energy. You have an electric source – a battery – that allows you to drive gas-free for an EPA-estimated 35 miles. And there’s also an onboard gas generator that produces electricity so you can go farther. So if you want to drive using only electricity, you can. If you want to drive using electricity and gas, you can do that, too. Feeling all charged up? Check out...