787 Batteries and Chargers - Part 1

[saptzae]

@RR_NDB

We may never understand WHY (BOS and TAK)

Yes, as we see only effects of Tertiary failures, which destroyed all evidence of degradation leading to the Primary failure.

• 6 Tertiary failure symptoms (heat, fire)
  • 5 Tertiary failure sequence (multi shorts, arcing)
    • 4 Secondary failure symptoms (multi-cell runaway)
      • 3 Secondary failure sequence (electrical or thermal)
        • 2 Primary failure sequence (cell short)
          • 1 Cell degradation

It's impossible to trace back from 6 to 1.

There seem to be no detailed records of per cell voltages around the time of Primary/Secondary failure, which would be the only way to conclusively determine sequence of Primary failure and cause of Secondary failure.

Looking at other in-service, or replaced batteries to find degraded cells is the only way.

Edit
Secondary failure should be reproducible by failing a Cell.

Tertiary failures should be mitigated by better electrical and thermal insulation of individual cells.