ITman:
I like the report in Flight Global especially the first paragraph...., this makes the whole thing very worrying.. Also noted that they are going for a higher discharge level that is a guarantee for battery heating and potential failure IMO.
I had a problem with that too, until I looked very hard at the description and realized that what he was referring to was stopping the discharge at a higher voltage/State Of Charge level rather than discharging more deeply.
Similarly on the high end, the are stopping charging sooner.
Together they will avoid larger parts of the battery operation area at either end that are most associated with both inefficiency and stress on the battery.
As a result the nominal energy capacity of the battery will be lower, but the available current will not be affected.
Oh, one other point while I am on the subject: When the aft battery is called on to deliver power, without the APU or other power available, does it also supply power to the charger and FDR so that conditions of discharge are recorded? Since they have had to replace so many batteries for over-discharge, that seems like relevant data.