NEW YORK — Federal investigations said Sunday that they had ruled out excessive voltage as the cause of a battery fire on a Boeing 787 in Boston this month, widening the mystery into what led to the grounding of the 787, the world’s most technologically advanced jet, after a second battery-related problem last week.
With investigators focused on the plane’s lithium-ion batteries, the National Transportation Safety Board said data from the flight recorder indicated the battery ‘‘did not exceed the designed voltage of 32 volts.’’ The fire aboard a Japan Airlines plane on Jan. 7 at Logan International Airport occurred after passengers had left.
On Wednesday, a battery problem on another 787 forced an All Nippon Airways jetliner to land in Japan. That prompted authorities around the world to ground the plane, known as the Dreamliner. The Federal Aviation Administration said it would not lift the ban until Boeing could show the batteries were safe. Its statement suggested there might not be a rapid resumption of 787 flights.
Speaking after the US safety board’s statement on Sunday, a Japanese investigator said their inquiry was not as far along as the American one.
GS Yuasa Corp., of Japan, makes the batteries for the 787, and Thales, of France, makes the control systems for the battery.