Japan's ANA replaced 10 Dreamliner batteries before emergency landing

All Nippon Airways said it had replaced 10 below-par lithium-ion batteries on its Boeing Co 787 Dreamliners in the months before one of the passenger jets was forced to make an emergency landing due to an overheated battery triggering smoke alarms.

The Japanese carrier, the biggest customer to date for the new Boeing jetliner, did not inform accident investigators in the United States because the incidents, including 5 batteries that had unusually low charges, did not compromise the plane's safety, ANA spokesman Ryosei Nomura said on Wednesday.

ANA did, however, inform Boeing of the faults that began in May, and returned the batteries to their manufacturer, GS Yuasa Corp. A spokesman for the battery maker declined to comment on Wednesday. Shares of the company fell 1.2 percent.

Boeing spokesman Marc Birtel said the airplane maker could not comment as the U.S. National Transportation Safety Board (NTSB) has indicated this is now part of their investigation.

The New York Times earlier quoted an NTSB spokeswoman as saying the agency would include these "numerous issues" with the 787 battery in its investigations.

Under aviation inspection rules, airlines are required to perform detailed battery inspections once every two years.

The global fleet of 50 Dreamliners - 17 of which are operated by ANA - remain grounded as investigators in Japan and the U.S. try to find out what caused one battery to catch fire on a Japan Airlines Co 787 at Boston's Logan Airport earlier this month, and a second battery to burn on the ANA domestic flight that made the emergency landing.

The NTSB said on Tuesday it was carrying out a microscopic investigation of the JAL 787 battery. Neither it nor the Japan Transport Safety Board has been able to say when they are likely to complete their work.