"ANA said it replaced 10 of the batteries in the months before [the recent incidents].
In five of the 10 replacements the main battery had showed an unexpectedly low charge. An unexpected drop in a 787’s main battery also occurred on the flight that had to make an emergency landing in Japan on Jan. 16.
In three instances, the main battery failed to operate normally and had to be replaced along with the charger. In other cases, one battery showed an error reading and another, used to start the auxiliary power unit, failed. All the events occurred from May to December of last year.
According to investigators in Japan, the battery on the jet that made the emergency landing showed a stable reading of 31 volts, near its full charge capacity, until 15 minutes into the flight when pilots detected a strange smell. About that time, sensors detected a sudden unstable discharge of the battery to near zero for reasons that Japanese investigators still cannot explain."
http://www.nytimes.com/2013/01/30/bu...pagewanted=all