TOKYO (AFP) - Officials probing the emergency landing of a Boeing Dreamliner said today they will dismantle its battery pack, after the investigation found no evidence of a sudden surge in voltage.

A fire risk from overheating powerpacks emerged as a major concern after pilots were forced to land the domestic All Nippon Airways (ANA) flight in western Japan on Jan 16 due to smoke thought to be linked to the plane's battery.

Investigators later released a picture showing the blackened remains of the battery in the ANA plane.

But they said today there were no signs of a battery fire, while data gleaned from the flight's digital data recorder showed the powerpack did not suffer a rapid surge in voltage.

The pack's voltage, in fact, had been at normal levels before it rapidly plunged just before the system alert that forced the emergency landing, a Japan Transport Safety Board (JTSB) official said.

But he said the pack - made up of eight individual lithium-ion batteries - would have to be dismantled to inspect each of the units, which are similar to those used in mobile phones and tablet computers.

"It was a very normal level of voltage for a lithium-ion battery (shortly before the emergency landing)," the official said.

"But you still cannot rule out the possibility that some of the individual batteries might have been overcharged." Officials from the JTSB and US National Transportation Safety Board would dissect the pack at the offices of Kyoto-based GS Yuasa, the maker of the next-generation aircraft's batteries, he said.

The powerpack's charger would be sent to its US manufacturer for a closer look, investigators said.

Boeing's fuel-efficient planes suffered a series of problems earlier this month, prompting a global alert from the US Federal Aviation Administration that has seen all 50 operational Dreamliners grounded since last week.