Investigators in the United States and Japan are examining how the Lithium-Ion main batteries in the 787 suffered a thermal runaway, or overheating that can burn a battery out and create a fire that is difficult to extinguish.

Reverting to less volatile Nickel-Cadmium would mean sacrificing improvements in weight in the lighter Lithium-Ion batteries, equivalent to one adult male passenger out of between 270 and 350 passengers and cargo on board.

But this is a fraction of the 40 tonnes saved by the A350 compared with older planes, according to company presentations.

“The penalty in weight compared with the risks associated with Li-Ion is minimal,” said Nick Cunningham, an aerospace analyst at Agency Partners in London.

Plane and battery makers say the technology is safe but recognize it is in the early stages of use in commercial flying.

Cunningham said Airbus and Boeing had learned from past development snags that it pays to tackle problems early rather than having to embark on costly refits that burn up cash.