Japan's two major airlines said Wednesday they had replaced a number of batteries in their Dreamliners after experiencing problems well before the worldwide grounding of Boeing's next generation plane.
A spokeswoman for All Nippon Airways said 10 batteries on its fleet had been switched, while a representative of rival Japan Airlines (JAL) told AFP "quite a few" had needed changing.
The lithium-ion batteries, made by Japanese manufacturer GS Yuasa, have been at the centre of a probe into the Dreamliner's airworthiness since a fire on a JAL plane in Boston and an emergency landing on an ANA flight in Japan.
ANA, the launch customer for Boeing's lightweight plane, had to replace batteries 10 times ahead of the January 16 emergency landing forced by smoke apparently linked to the powerpack, company spokeswoman Naoko Yamamoto told AFP.
The airline, which started operating Boeing 787s in November 2011, had to replace some batteries after only a week while others lasted only a month, she said.
In four cases, the main powerpack was only partially charged, while in two other cases a battery or an auxiliary power unit -- which boosts the battery -- failed to start, she said.
All 10 replacements occurred last year -- two in May, four in October, two on one day in November and two in December -- involving seven Dreamliners, she said. The airline operates 17 of the planes.
ANA had not reported the replacements to the Japan Transport Safety Board (JTSB) because "the ten problems were found before flights so were considered not to affect safety", Yamamoto said.
A JAL spokeswoman said the company had experienced "quite a few cases" where Boeing 787 batteries had to be replaced before the aircraft was grounded worldwide. She added that no further details were immediately available.
GS Yuasa, the Kyoto-based manufacturer of the lithium-ion battery, said it could not comment on how long the product is designed to last.
However, in the days after the emergency landing in western Japan, ANA said the particular battery involved had been installed in October, ahead of the expected two-year replacement cycle.
Aviation regulators have released a picture showing the blackened remains of the battery that inspectors removed from the plane.
But they said last week there were no signs of a battery fire, while information gleaned from the flight's digital data recorder showed the power pack did not suffer a rapid surge in voltage.
The pack's voltage, in fact, had been at normal levels before it rapidly plunged ahead of the system alert that forced the emergency landing, a JTSB official told AFP last week.
GS Yuasa is just one of many contractors in a complex global chain that led to three years of delays before Boeing delivered its first 787 to ANA in 2011.
US regulators have said they will not allow the 787 to fly again until they are sure the problems around the battery system have been fixed.
The worldwide grounding of the next-generation plane is having an increasing effect on airlines flying it.
ANA has reportedly cancelled 838 flights, affecting nearly 83,000 domestic and international passengers, over the period to the middle of next month.
ANA and JAL are important Dreamliner customers who have so far ordered a combined 111 aircraft.