TURIN
That seems to be good enough reason to ground it.
The use of Li Ion batteries on airliners is under investigation. This should be enough to make other authorities to address the issue.
Important to differentiate the cells to the battery:
E.G.
The 787 battery is made by Thales using cells from Yuasa.
AFAIK the battery used in A380 emergency lightning comes from SAFT. The details will be commented in another thread.
TacomaSailor,
Important issue:
"individual cells having excessive internal resistance which raised their internal voltage and leads to thermal runaway in that one cell."
I will go further: You need to monitor ea. cell voltage AND temperature, during charge AND discharge. This is critical (safety) and important for longer life. I (strongly suspect) have serious objections how they are using the cells.
The safest would be to separate them (redundantly) electrically and physically. This will be addressed in
787 Batteries and Chargers