If it is only battery safety that is concerning the FAA, I wonder if replacing the Yuasa battery with an equivalent SAFT Li-ion unit would work as an interim 'fix' to get the 787 fleet in the air again.
SAFT seem to have a good safety and reliability record in the supply of LI-ion batteries for use in space vehicles. For this application, they must be capable of withstanding mechanical stresses during launch and a wide temperature range during orbit. Safety features on individual SAFT cells include a shutdown separator, a circuit breaker, a vent and a stainless steel outer case. A SAFT battery, comprising a number of individual cells, is then encased in a further stainless steel container.
See link:
http://www.saftbatteries.com/doc/Doc...e4af5b011d.pdf