(CBS News) WASHINGTON - CBS News has learned that more than just a few batteries went bad on Boeing's revolutionary Dreamliner 787s since the airliner began flying over a year ago.
Two overheated batteries, one leading to a fire, grounded the fleet earlier this month while investigators look into the cause. New details are a sign the problem was much more widespread.
United Airlines had to replace multiple batteries on its fleet of six Dreamliners.
United has only been flying the Dreamliner since early November, so aviation safety experts say it's a red flag that more than one battery would already be having trouble.
Japan's All Nippon Airways issued a statement: "We had 10 cases of battery replacement due to technical issues in 2012. None of the 10 cases were considered a safety issue with no reporting requirements to the government, and no flights were cancelled or delayed. This frequency is the same level as 777 or other types of aircraft in recent years, and we do not see this number outstandingly high."
ANA said half the replaced batteries showed an unusually low charge, which could be important because when lithium ion batteries drain too low, recharging can create a fire risk.
The Dreamliner has been flying for ANA for over a year
On Wednesday, Boeing told CBS News that battery replacements are not "a result of safety concerns" but part of procedures that ensure faulty batteries aren't kept in circulation.
CBS News has also learned that FAA confirmed Boeing did not report to them the battery issues that led ANA and other carriers to swap them out, but notes that they were not required to as the issues did not meet the standard for "mandatory reporting."