The NTSB says it will finish its detective work on the Boeing 787 lithium-ion batteries in March and will issue the final report and hold a public hearing this fall on the January 2013 Japan Airlines incident that spawned the investigation.

A second battery failure led to the FAA’s grounding of the fleet one year ago this month.

“Members of the investigative team have been conducting work in the United States, Japan, France, and Taiwan,” says the NTSB in its latest update on the investigation, released today. “As the investigation has progressed, the NTSB has been working closely with Boeing, the FAA, the Japan Transport Safety Bureau, the French BEA, and technical advisors from Japan and France.”

Japan-based GS Yuasa builds the 787 batteries, the first application of large-scale lithium-ion technology in commercial aircraft, and Thales builds the charging system.

In the Japan Airlines incident, the 787’s auxiliary power unit (APU) lithium-ion battery caught fire after an internal cell failure while the aircraft was on the ground in Boston on Jan. 7, 2012, with no passengers or crew on board. A week later, the main lithium-ion battery on an All Nippon Airlines 787 failed in flight, causing the pilots to divert. The FAA issued an emergency airworthiness directive on Jan. 16 that grounded the nascent fleet of 50 aircraft and scuttled deliveries of new 787s.

In parallel with the NTSB investigation, which included a two-day investigative hearing in April, Boeing developed fixes to the batteries, including new containment and venting systems as well as modified charging systems. The modification package was approved by the FAA and installed in the fleet. By June, all aircraft were once again flying with no reported instances of main or APU batteries since.

Despite the apparent success of the battery fix, the NTSB continues to investigate battery design and operation and will issue its probable cause finding in the final report, most likely along with recommendations for Boeing and the FAA to prevent future problems with introducing new technologies.

Included in the on-going work includes a contract to Underwriter’s Laboratories for characterizing the thermal and electrochemical properties of the battery and performing “oscillatory testing,” both of which will be complete in February.

In total, the NTSB says it has conducted more than 200,000 computed tomography scans of battery cells “to examine and document the internal configuration of individual cells from the incident and exemplar batteries.”