NTSB stated Feb 1:
The auxiliary power unit battery, manufactured by GS Yuasa, was the original battery delivered with the airplane on December 20, 2012. It is comprised of eight individual cells. All eight cells came from the same manufacturing lot in July 2012. The battery was assembled in September 2012 and installed on the aircraft on October 15, 2012. It was first charged on October 19, 2012.
Examination and testing of an exemplar battery got underway earlier this week at the Carderock Division of the Naval Surface Warfare Center laboratories in West Bethesda, MD. The tests consisted of electrical measurements, mass measurements, and infrared thermal imaging of each cell, with no anomalies noted. The cells are currently undergoing CT scanning to examine their internal condition. In addition, on Thursday, a battery expert from the Department of Energy joined the investigative team to lend his expertise to the ongoing testing and validation work.
An investigative group continued to interpret data from the two digital flight data recorders on the aircraft, and is examining recorded signals to determine if they might yield additional information about the performance of the battery and the operation of the charging system.
Next week, the NTSB battery testing team will initiate a non-invasive "soft short" test of all cells of the exemplar battery. This test will reveal the presence of any high resistance, small or "soft" shorts within a cell. Also, an NTSB investigator will travel to France with the battery contactor from the JAL event battery, for examination at the manufacturer. The battery contactor connects a wiring bundle from the airplane to the battery.