In their interim report, section 1.5.4, the NTSB reports having made Computed Tomography (CT) scans of both the APU battery that burnt, and "the main battery (that) was used as an exemplar battery for the radiographic studies". This sentence strike me:
The CT scans for the main battery showed no anomalies outside the cells.
And, in the "Ongoing and planned investigation activities, this one:
Document the results of the CT scans of the individual cells from the main battery.
Any interpretation of that?