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U.S. aviation-safety investigators said early Sunday there was no voltage surge when a lithium-ion battery caught fire Jan. 7 aboard a Boeing 787 at Logan International Airport in Boston.

The National Transportation Safety Board said flight recorder data from the Japan Airlines plane showed the battery “did not exceed its designed voltage of 32 volts.”

Investigators in the U.S. and Japan are probing the batteries at the center of two incidents that led to the dramatic grounding of the worldwide fleet of 787s. The Federal Aviation Administration and regulators elsewhere ordered the grounding after a second incident in Japan on Jan. 16 involving the lithium ion batteries that produce electricity for the plane’s auxiliary power units (APUs).

Boeing has said its battery system has controls to prevent excessive charging or discharging, which is one possible cause for the battery incidents.

The NTSB released no other conclusions, but detailed how the eight-cell lithium ion battery and related electrical equipment have been dismantled by investigators for further study, including x-ray and CT scans.

“On Tuesday, the group will convene in Arizona to test and examine the battery charger and download nonvolatile memory from the APU controller,” the NTSB statement said. “Several other components have been sent for download or examination to Boeing’s facility in Seattle and manufacturer’s facilities in Japan.”