No obvious anomalies are reported to have been found in a second battery on a Boeing 787 Dreamliner after a fire at Boston airport.

The US National Transportation Safety Board said that at the time of the fire earlier this month the Japan Airlines aircraft had completed 22 flights and 169 flight hours.

The board’s update said that investigators had completed a review of two systems associated with the auxiliary power unit, at two locations in Arizona, and found no problems.

The second battery was of identical design to the one destroyed but is 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, according to news agency Reuters.

The board said its laboratory was continuing to study the destroyed battery. Its function was to start the auxiliary power unit, a small jet engine used mostly on the ground. The battery, which was not being charged or discharged, caught fire while the plane was empty.

The undamaged battery on which the board reported Sunday was a backup for cockpit instruments, located near the nose.