Investigators examining the battery used onboard the Boeing Dreamliner 787 have discovered no faults with the component.
Officials at the transport ministry in Japan said attention had now shifted to the electrical system that monitors battery voltage, charging and temperature.
The battery was initially considered the likely source of problems on 787s owned by two Japanese airlines.
Transport ministry official Shigeru Takano told the BBC: “We have found no major quality or technical problem with the lithium-ion batteries.”
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 Logan Airport in Boston.
Having ruled out the battery as a cause of the incidents, Boeing, alongside investigators from the United States and Japan, may now need longer to discover the cause of the problem.
This poses the threat of a prolonged grounding for the Dreamliner.
Analysts have warned aviation regulators will have to put the 787 through another airworthiness certification process.
This could become a complicated and lengthy process depending on the final cause of the problem.
Boeing has orders for more than 800 Dreamliners.