Over the last two years, the federal government has doled out nearly $2.5 billion in stimulus dollars to roughly 30 companies involved in advanced battery technology. Many of these might seem less like viable businesses than scenery for political photo ops — places President Obama can repeatedly visit (as he did early this month) to demonstrate his efforts at job creation. But in fact, the battery start-ups are more legitimate, and also more controversial, than that. They represent “the far edge,” as one White House official put it, of where the president or Congress might go to create jobs.