NEW YORK — Even before two battery failures led to the grounding of all Boeing 787 jets this month, the lithium-ion batteries used on the aircraft had experienced multiple problems that raised questions about their reliability.
Officials at All Nippon Airways, the jets’ biggest operator, said in an interview Tuesday that it had replaced 10 of the batteries in the months before fire and smoke in two cases caused regulators around the world to ground the jets.
The airline said it had told Boeing of the replacements as they occurred but had not been required to report them to safety regulators because no flights were canceled or delayed. National Transportation Safety Board officials said Tuesday that the replacements were now part of their inquiry.
The airline also, for the first time, explained the extent of the previous problems, which underscore the volatile nature of the batteries and add to concerns over whether Boeing and other plane makers will be able to use them safely.
In five of the 10 replacements, All Nippon said that the main battery had showed an unexpectedly low charge. An unexpected drop in a 787’s main battery also occurred on the All Nippon flight that had to make an emergency landing in Japan on Jan. 16.
The airline also revealed that in three instances, the main battery failed to operate normally and had to be replaced along with the charger. In other cases, one battery showed an error reading and another, used to start the auxiliary power unit, failed. All the events occurred from May to December 2012. And all the batteries were returned to their maker, GS Yuasa.
Kelly Nantel, a spokeswoman for the NTSB, said investigators had only recently heard that there had been ‘‘numerous issues with the use of these batteries’’ on 787s. She said the board had asked Boeing, All Nippon, and other airlines for information about the problems.
“That will absolutely be part of the investigation,” she said.
Boeing, based in Chicago, has said repeatedly that any problems with the batteries can be contained without threatening the planes and their passengers.
But in response to All Nippon’s disclosures, Boeing officials said the airline’s replacement of the batteries also suggested that safeguards to prevent dangerous overheating of the batteries might have kicked in.
Boeing officials also acknowledged that the new batteries were not lasting as long as intended. But All Nippon said that the batteries it replaced had not expired.
A GS Yuasa official, Tsutomu Nishijima, said battery exchanges are part of the normal operations of a plane but would not comment further.
The Federal Aviation Administration decided in 2007 to allow Boeing to use the lithium-ion batteries instead of older, more stable types as long as it took safety measures to prevent or contain a fire. But once Boeing put in those safeguards, it did not revisit its basic design even as more evidence surfaced of the risks involved, regulators said.
In a little-noticed test in 2010, the FAA found that the kind of lithium-ion chemistry that Boeing planned to use — lithium cobalt — was the most flammable of several possible types. The test found that batteries of that type provided the most power, but could also overheat more quickly.