At a guess, 98 per cent of the discussion here is 100% forensic debrief.
Were I Boeing, that is where I would like the discussion to be.
Likewise Yuasa.
The manufacture of the Yuasa Batteries requires meticulous handwork, scrupulously clean surroundings, and exquisitely pure ingredients and materials.
The CT scans of sections of even the JAL exemplar show problematic bunching, packing, and wrinkling of the electrode stack. Given the design, the geography of the enclosure, and its attendant kit, to ignore the probability that failure is merely a shortened service life due environmental impacts is not far fetched.
On the face of it, that is what Boeing determined, hence the AFR (Accelerated Field Replacement).
It's Friday evening. I'm down to the local for a pint. Maybe I'll run into W. Occam, kick this around.....