Investigators said the power supply battery that caught fire in a Japan Air Lines (JAL) Dreamliner in Boston was not faulty, and that problems could still exist with wiring or other charging components.
An examination of the flight data recorder indicated that the battery did not exceed its designed voltage of 32 volts, the US National Transportation Safety Board (NTSB) said in a statement.
Meanwhile in Japan, investigators are conducting a probe of the maker of the lithium ion batteries used in Boeing's grounded 787 jets.
GS Yuasa battery spokesman Tsutomu Nishijima confirmed that the investigators visited the company's headquarters in Kyoto, and the company was cooperating with the officials.
He said he could not comment on details of the investigation or on whether it would continue beyond Monday, and transport ministry officials also would not comment on the probe or its findings.
NTSB investigators in the US continue to look at the wider battery system and plan to meet officials from Securaplane Technologies, the Arizona-based manufacturer of the charger for the plane's lithium ion batteries.
NTSB spokeswoman Kelly Nantel said: "Potentially there could be some other charging issue - we're not prepared to say there was no charging issue."
Even though it appears the voltage limit was not exceeded in the plane emergency on January 7 in Boston, it could be behind a later event.
Last week an All Nippon Airways (ANA) plane made an emergency landing in Japan which may have been because of a charging problem, according to ex-NTSB board member and aviation safety expert John Goglia.
Too much current flowing too fast into a battery can overwhelm the unit, causing it to short-circuit and overheat, even if the battery's voltage remains within its design limit, he said.
"The battery is like a big sponge," Goglia said.
"You can feed it with an eye dropper or you can feed it with a garden hose. If allowed, it will soak up everything it can from the garden hose until it destroys itself."
There are so many redundancies and safeguards in aviation that when an accident or mishap occurs, it is almost always the result of a chain of events rather than a single failure, he said.
On January 16, the ANA flight made an emergency landing in western Japan after a cockpit message warned of battery problems and a burning smell was detected in the cockpit and cabin.
An investigator in Japan last Friday said that the burned insides of the plane's lithium ion battery show the battery received voltage in excess of its design limits.
Boeing's composite construction aircraft has suffered a string of faults recently – reaching a total of six separate incidents in little more than a week.
Since then, all 50 787s that Boeing has delivered to airlines have been grounded, and deliveries of new planes have been halted until it can address the electrical problems.
The batteries in two incidents "had a thermal overrun because they short-circuited," Mr Goglia said.
"The question is whether it was a manufacturing flaw in the battery or whether it was induced by battery charging."
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