@hetfield
I though more about the practical side of detecting, in a timely manner, a short of a sub-cell. At that time, the BMS can't stop the cell failure, but it must protect the other cells by taking the battery off-line.
A short will not be static, it starts at a spot, current, temperature and pressure increase, it may even "burn out", but damage done will lead to further shorts nearby, propagate and short resistance will be transient with a reducing trend.
As you pointed out, a shorting sub-cell will "fight" five good sub-cells.
Thus, the the voltage variations seen by the BMS may be quite small and it may not respond in a timely manner.
What is timely? I am not sure, a few milliseconds at the most, below 100 microseconds would be better. Such short response time is difficult to accomplish.
Summing up, your concern about managing sub-cell shorting is valid, and i see your interpretation as a practical explanation for why a single cell short propagated to other cells.
What has to be done, is to make the BMS more sensitive to voltage transients on individual cells and shut charging down very quickly.
Last edited by saptzae; 6th Feb 2013 at 12:46.