Last March, in the comments section of an article in Aviation Week was the following comment;
Bayanist
1:55 PM on 3/29/2013
I guarantee that the 787 problem is not with the battery technology but with the assumption that it is possible to charge as many as 8 cells in series without problems. The weakest cell WILL reverse polarity and appear as a short after the fact. This is true for any battery technology. I have done it with diehard lead acid batteries. To be safe each cell must be charged individually. Otherwise it is similar to pushing a chain. Unless each link is PERFECTLY aligned there will not be success. Unless each cell is PERFECTLY matched there will not be success. Since this is clearly impossible in this universe there will be future problems unless my warning is heeded. Time will prove me correct, Of that I am certain. Watch and see!
Source;
787 ETOPS Threat Dismissed As Speculation
I'm not sure whether the battery redesign changed this aspect or not. If it didn't then perhaps this is the cause of the issue?