WASHINGTON — Although a fire destroyed one of two big batteries on a Boeing 787 parked at Logan International Airport in Boston three weeks ago, a quick examination of the second battery found ‘‘no obvious anomalies,’’ the National Transportation Safety Board said Sunday.

The second battery was of identical design but used for a different purpose than the first, the agency said. Its report added scattered details to what is known about the incident, one of two battery problems that led to the grounding of all 50 of the 787s in airline service.