In Japan on Thursday, government investigators examined the 787 that made the emergency landing. Footage on the public broadcaster NHK showed officials removing a charred and swollen lithium-ion battery pack from the front of the plane.

Corrosive liquid appeared to have leaked out of the batteries, leaving streaks on their blue casing, said Hideo Kosugi, a safety official who is head of the inquiry. Investigators also found black discolorations outside exhaust vents on the plane, which suggested that there had been smoke inside the aircraft at one point.

“The batteries have retained their basic shape, but are black all over,” Mr. Kosugi said. Something caused the battery to overheat and spew liquid, he added, “but we still do not know what is the cause.”

The 787 uses two identical lithium-ion batteries, each about one and a half to two times the size of a typical car battery. One battery, in the rear electrical equipment bay near the wings, is used to start the auxiliary power unit, a small engine in the tail that is used most often to provide power for the plane while it is on the ground. The other battery, called the main battery, starts the pilot’s computer displays and serves as a backup for flight systems.

The maker of the 787’s batteries, GS Yuasa of Japan, has declined to comment on the problems.

Boeing has defended the novel use of the batteries and said it had put in place a series of systems meant to prevent overcharging and overheating.

In a conference call last week with reporters, Boeing’s chief engineer for the 787, Mike Sinnett, said that the company had long been aware of possible problems with lithium-ion batteries but that it had built in numerous redundant features to keep any problems with the batteries from threatening the plane in flight. He said that the batteries had not had any problems in 1.3 million hours of flight and that Boeing was trying to understand what had caused the problems.

Mr. Sinnett said that if the lithium-ion batteries started a fire, it would be nearly impossible to put out because the batteries produce oxygen when burning. Mr. Sinnett said that the plane was designed to survive such an event in flight, when the cabin’s air-pressure system protects passengers and allows the plane to vent the smoke outside. The plane is also designed, he said, to contain a fire to a small area.