Boeing says it 'may never find the cause of 787 Dreamliner battery fault' 22 April 2013 Last updated at 14:03 By Will Smale Business reporter, BBC News Boeing has admitted that it may never know what caused the battery malfunctions that resulted in all its 787 Dreamliner aircraft being grounded. The admission came from Boeing's Larry Loftis, the general manager of the company's 787 division. Replacement battery systems are now being fitted to all 50 Dreamliners that had been in operation with airlines around the world. Boeing expects the planes to resume service in the coming weeks. On Friday last week, US aircraft regulators approved a revamped battery design for the aircraft, paving the way for the fleet to return to the skies. Speaking at a media briefing in London, Mr Loftis said: "It is possible we will never know the root cause. It is not uncommon not to have found the single root cause. So industry best practice is to look at all the potential causes and address all of them. The groundings of all Dreamliners in January followed two major incidents concerning the plane's two lithium-ion batteries. Firstly, on 7 January, a battery overheated and started a fire on a Japan Airlines 787 at Boston's Logan International Airport. Nine days later, an All Nippon Airways 787 had to make an emergency landing in Japan after a battery started to give off smoke.