Japan's transport ministry has said the airline safety inspectors have found no faults with the battery used on Boeing's 787 Dreamliner.
The battery was initially considered the likely source of problems on 787s owned by two Japanese airlines.
It has raised fears that there will be no quick solution to the problem, which led to all 50 787s in service to be grounded, the BBC reports.
Attention has now shifted to the electrical system that monitors battery voltage, charging and temperature.
Transport ministry official Shigeru Takano said that they have found no major quality or technical problem with the lithium-ion batteries.
He added that they were now are looking into affiliated parts makers, adding that they were looking into all possibilities.
The safety investigation started after one of the 787s operated by All Nippon Airways made an emergency landing in Japan when its main battery overheated.
Earlier, a battery in a Japan Airlines 787 caught fire while parked at Boston's Logan International Airport.
Keith Hayward, head of research at the Royal Aeronautical Society, said that if the issue is no longer about replacing a faulty battery, it raised the prospect of Boeing having to do a major re-design.
According to the report, he added that aviation regulators will have to put the 787 through another airworthiness certification process, which itself could become a complicated and lengthy process depending on the final cause of the problem.
Two weeks ago the US Federal Aviation Administration said both batteries had leaked electrolyte fluid, and there had been smoke damage to parts of the aircraft.
The FAA said airlines must demonstrate battery safety before flights could resume, a statement that effectively meant airlines had to ground their 787s.
Boeing, which competes against Europe's Airbus, has halted 787 deliveries. Boeing has orders for more than 800 Dreamliners.
The 787 is the first airliner made mostly from lightweight composite materials, which increases aircrafts fuel efficiency.
It also relies on electronic systems rather than hydraulic or mechanical systems to a greater degree than any other airliner, the report added. (ANI)