Infusion from Buffett helps bank

Bank of America rallied after Warren Buffett’s Berkshire Hathaway invested $5 billion. Buffett said he reached out to CEO Brian Moynihan because he considered the bank a “strong, well-led company.’’ Lately, the market has rendered a different verdict. As recently as Tuesday, its stock had plunged 50 percent from a year ago on concerns over its mortgage problems and worries that it would have to sell lots of stock to shore up its balance sheet. It is the largest US bank and has nearly 300 Bay State branches.