Officials at All Nippon Airways, the Dreamliner's biggest operator, told The New York Times Tuesday it replaced 10 of the lithium-ion batteries in the months prior to two incidents that prompted regulators to ground the jets worldwide.
The officials said they told Boeing of the replacements but weren't required to report them to safety regulators because matters weren't considered a safety issue and flights weren't affected.
National Transportation Safety Board officials said Tuesday their inquiry would look into the replacements.
All Nippon also outlined the scope of previous problems, drawing attention to the volatility of the lithium-ion batteries and raising questions about whether airplane manufacturers can use the lighter weight batteries safely, the Times said.
All Nippon said the main battery showed an unexpected low charge in five of the 10 replacements. In three instances, the main battery and its charger had to be replaced because they failed to operate normally, among other things.
NTSB spokeswoman Kelly Nantel said investigators only recently learned of the "numerous issues with the use of these batteries" on 787s and had asked All Nippon and other carriers about the problems.
"That will absolutely be part of the investigation," she said.
Boeing, based in Chicago, has said any problems with the batteries could be addressed without threatening the airplanes and passengers. In response to All Nippon's disclosures, however, Boeing said the airline's replacement of the batteries suggested safeguards had been activated.
An official for GS Yuasa, the battery manufacturer, said battery exchanges were considered part of the normal airplane operations but declined further comment, the Times said.