As a savvy EE I strongly recommend expanding the root cause search for the 787 battery problem beyond the batteries themselves. The root cause could be an unintended operating mode in charger or protection circuits.
In the mid 1990s, a significant portion of the analog IC industry began experimenting with various bonus schemes to improve new-product time to market and stock performance. But analog ICs are cantankerous beasts and multiple revisions for new designs proved necessary regardless of the incentives. The net result was pressure to cheat by pushing defective products to market for bonuses.
I was employed in a new-product verification role at the time and was often the last line of defense in quality regarding bugs. There was begging, scheming, falsification of test data and outright threats to my employment made to get defective products past me. And I was terminated in retaliation for standing my ground on quality.
Since then, I've seen an industry-wide loss of new-product bug testing talent. And I've seen many bugs making it to market. For example, one analog IC had two battery chargers for Lithium-Ion cells. One of the chargers had a floating node that caused the charger's current to very slowly ramp from microamperes to amperes over the course of hours despite the charger being off. That IC is not in the 787 because it failed on the market due to other bugs and was obsoleted. But its a good example illustrating my advice.
Floating nodes and such problems are very difficult to find in analog ICs because they exhibit themselves in an intermittent, non-deterministic way. The one I found was only caught because I was paying close attention while characterizing other attributes of the new-product. The initial symptoms were so subtle that 999/1000 engineers would have missed them and I almost did. There was only a slow monotonic increase in the values of the lowest digits of the 6 digit DMM. But I was the best of the best in my trade at that time and it was a lucky day.
Best wishes in fixing the unfortunate problem in your otherwise fine new plane.
I would want to instrument and flight test one or both of the two aircraft that exhibited the battery problems. Also add a form of fire suppression as part of the flight test instrumentation for additional safety. A thorough sneak-path analysis and failure modes analysis on the battery systems are hopefully in-process.