Detailed examination of the ELT [emergency locator transmitter] has shown some indications of disruption to the battery cells. It is not clear however, whether the combustion in the area of the ELT was initiated by a release of energy within the batteries or by an external mechanism such as an electrical short.
In the case of an electrical short, the same batteries could provide the energy for an ignition and suffer damage in the subsequent fire.
Ethiopian Airlines said it would continue to operate its fleet of Boeing 787 Dreamliners after one of them caught fire at Heathrow airport.
The company's public relations department said: "We have not grounded any of our aircraft. The incident at Heathrow happened while the plane was on the ground and had been for more than eight hours and was not related to flight safety."
Asked whether the airline has determined the cause of the fire, Ethiopian Airlines said: "There is no new development. No safety issue. The incident is being investigated to determine cause of smoke."
A passenger on a Manchester Dreamliner flight has described to ITV News how they noticed the plane had been turned around on the in-flight displays before the pilot told them they were returning.
The passenger, who preferred not to be identified, told Richard Edgar: "The concern of a lot of passengers was that when the plane had landed we were kept on board the plane for twenty minutes, by this time people had found out that the Dreamliner from Ethiopian Airlines had been on fire."