Bank of America Corp, the biggest US bank by assets, raised about $13.5 billion by selling new shares after US regulators determined it needed more cash to weather the economic condition.   The Charlotte, North Carolina- bases company issued 1.25 billion shares at around $10.77 each, according to a statement yesterday, and plans to boost common equity capital by $17 billion through the sale of stock and converting preferred shares mostly held by institutional investors, chief executive officer Kenneth Lewis said earlier this month.