One of the parameters the FAA requires is an overcharge test that can induce thermal runaway. The FAA needs to understand how this develops regarding heat generation, fire, and outgassing. Airbus refusal in making this test is based on theirs and their battery manufacturer's belief that the A350 batteries are
immune to overcharging. As the FAA and industry learned with Boeing, Yuasa, SecuraPlane, and Thales on the 787 batteries, never say never.
The overall designer for the 787's electrical system, and chooser of a Lion type battery for the 787 is a French company, working with two American companies providing the integration and charging electronics, and a Japanese battery company. That is a fairly cosmopolitan group. Comments regarding nationalism/NIH beliefs are not applicable here.
If it is true that the steel confinement weighs about as much as one pax, and if the choice of lithium batteries over nicads is driven by weight, is there any net advantage for lithium?
Batteries can be charged quicker, have no memory issues from partial charges/discharges and as already mentioned, dramatically higher energy density over NiCads.