(TOKYO) -- Lithium-ion batteries on board Boeing's 787 Dreamliners were plagued by problems long before battery failures grounded the planes earlier this month.
Published reports say All Nippon Airways replaced 10 of its batteries months ago because they failed to operate normally. In one case, they showed an unexpectedly low charge.
ANA notified Boeing but wasn't required to report the problem to safety regulators because it wasn't considered a flight risk.
The National Transportation Safety Board says past problems will be included in a larger investigation that has grounded Dreamliners indefinitely around the world.
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