Boeing has confirmed that a single cell of a Japan Airlines 787 lithium-ion battery overheated with the aircraft parked at Tokyo Narita International airport on 14 January.

“The issue occurred during scheduled maintenance activities with no passengers on board,” Boeing says in a statement. “The improvements made to the 787 battery system last year appear to have worked as designed.”

Boeing shares fell 4% immediately following a published report about the latest 787 lithium ion battery failure.

Within an hour the company’s shares had recovered to nearly $140 each, but that was still below the $142 price per share prior to the report.

According to a Reuters story, Japan Airlines says maintenance workers found smoke coming from the main battery of the 787.

The workers also found an unidentified liquid coming from the battery, the report says.

The report comes exactly one year and one week after a Japan Air Lines 787 parked at Boston Logan airport had a battery failure.

That incident involved the lithium ion battery used to start the auxiliary power unit, one of two rechargeable, 32V lithium ion batteries installed in the 787 and installed in the aft electronics equipment bay. Each battery contains eight powerful lithium ion cells, comprised of a lithium-cobalt-dioxide chemistry.

The main battery, which is located in the forward electronics bay beneath the cockpit, is used as a back-up power supply for the avionics.

Eight days after last year’s incident on the Japan Airlines 787, the main battery overheated in flight on an All Nippon Airways 787 and forced and emergency landing.

The US Federal Aviation Administration grounded the US 787 fleet the next day, a move that was copied by regulators around the world.

The grounding order was lifted four months later after Boeing designed an improved battery installation, including modifications within the batteries that are supposed to prevent overheating in anyone cell from triggering a thermal runaway and an intense fire.

One of the modifications included installing piping to directly vent any smoke from an overheated battery offboard the aircraft.

The new incident is the first confirmed venting of one of the lithium ion battery’s eight cells since the new design was installed last May.

A non-rechargeable lithium ion battery malfunctioned last July on a Ethipian Airlines 787 parked at London Heathrow airport, but that system was not unique to the aircraft and is unrelated to the previous failures.

The US National Transportation Safety Board (NTSB) plans to issue a probable cause on last year’s Japan Airlines lithium ion battery failure in Boston by the end of this year. Investigators in that incident are wrapping up their investigation by the end of March.

The Japan Transport Safety Board will have jurisdiction if an investigation is launched on the latest 787 battery problem.