A US investigation into a fire on a Boeing Co 787 Dreamliner in Boston earlier this month has found damage to a battery.

The US National Transportation Safety Board tonight said its investigation had revealed some thermal damage to all eight cells in a special lithium-ion battery used to generate auxiliary power for the plane.

Deborah Hersman, chairman of the safety board, and other NTSB officials will provide an update on the investigation at a news conference tomorrow, according to an NTSB news release.

The agency on Sunday ruled out overcharging as the cause of the battery failure.

The implications of the thermal damage cited by the NTSB are not immediately clear.

The NTSB said the battery, made by Japanese company GS Yuasa Corp, had eight cells of 3.7 volts each, and all eight had varying degrees of thermal damage.

Investigators have CT scanned and disassembled six of the eight cells, and their electrodes were being photographed and examined under a microscope, the agency said.

The remaining two batteries will be examined in the same way in the coming days at the agency's Washington laboratory.

Members of the investigative team had also been working in Arizona, Seattle and Japan, the NTSB said in a brief statement, without providing any additional details.