The cause of a series of problems with Boeing's new Dreamliner is still unknown after a joint US and Japanese investigation found no faults with the battery.
The battery was initially considered the likely source of problems on the planes owned by two Japanese airlines.
All 50 of the Boeing 787s in use around the world are grounded after one of the jets operated by All Nippon Airways made an emergency landing in Japan when its main battery overheated.
Earlier in January, a battery in a Japan Airlines 787 caught fire while the plane was parked.
