Japan Airlines is investigating what caused a battery on a Boeing 787 to emit smoke during preflight maintenance, a year after a fire on one of the carrier's Dreamliners helped spur the grounding of the global fleet.

Mechanics found that one of eight battery cells had vented liquid through a safety valve Monday, while the others were intact, JAL spokesman Seiji Takaramoto said.

Instruments in the cockpit showed a possible fault in a main battery and a main battery charger, he said.

The incident is the first sign of a battery failure since Boeing redesigned the units after a pair of meltdowns on 787s, one flown by JAL and the other by All Nippon Airways.

U.S. safety regulators said Tuesday that they were working with their peers in Japan to review the episode, which occurred on an empty jet at Narita International Airport.

"Damage was limited to one cell," said Hans Weber, president of Tecop International Inc., a San Diego-based consultant. "Something was wrong and fumes vented, as they are supposed to be. Very importantly, the system designed to isolate these neighboring battery cells from one another worked also."

Smoke was detected under the 787 during routine maintenance before a flight to Bangkok, spurring the hunt for the source, Takaramoto said.

JAL switched out that Dreamliner with another 787 for the flight, he said.

The two failures of lithium-ion batteries on Dreamliners in January 2013 prompted regulators worldwide to order the jets parked while Chicago-based Boeing crafted a fix.

GS Yuasa Corp., based in Kyoto, manufactures the batteries.