From the New York Times:

Japanese investigators, however, have maintained that there is still not enough evidence to show that the batteries themselves are the cause of fires, and that a shock could have caused them to overheat.

The Japanese have a vested interest in the batteries themselves NOT being the problem. The government actively subsidizes various industries involved with the 787 production including GS Yuasa, the maker of the Li-ion batteries used in the 787.

It should be interested to see how the FAA and Japanese review and approvals coincide with each other… or not.