A national charity will for the first time buy medical debt, totaling $278 million, directly from hospitals, a push to speed financial relief to patients, many of whom shouldn’t have been billed at all under the hospitals’ financial-aid policies. RIP Medical Debt, which uses donations to wipe out unpaid medical bills, has reached a deal with nonprofit Ballad Health, a dominant hospital system in Tennessee and Virginia, to buy debt owed by 82,000 low-income patients. Many likely qualified for free care under Ballad’s policy but didn’t get it, executives at Ballad involved in the agreement said.