Source: report on a Boeing presentation
Boeing outlines fix for 787 batteries ? The Register
(...Boeing) hinted, during a 90-minute
presentation and Q&A session in Tokyo, that a “deep discharge” event occurred in one cell of the planes' batteries, heating it to the point at which it vented so much hot electrolyte that an adjacent cell warmed and also vented. A manufacturing fault seems to be the reason such an event was able to occur (...)
Seems not unreasonable to me. Deep discharge of a cell is known to have the potential to leave it in a state of high internal resistance, where current flowing thanks to either the other cells supplying power, or a recharge attempt, will generate a lot of heat in the cell, causing the effect described.
If that is, several things went wrong
- operating procedures and supervising means should prevent using the battery beyond the point where deep discharge of all elements occurs; and only a defect of a cell should make deep discharge of a single cell possible (as hinted above);
- deep discharge of a single cell (always possible, and a clearly dangerous situation) could be detected by the electronics built into the battery, and trigger a fail-safe mode; if that's not designed-in, that's a mistake for a powerful battery, IMHO; and if it is there and did not work, why?