Dreamliner: Japan's airlines say they changed batteries
Japan's two top airlines said they had replaced a number of batteries in the 787 Dreamliners over the past months.
All Nippon Airways said it changed batteries 10 times. Japan Airlines (JAL) said it did so in a "few cases".
Earlier this month, a battery in a JAL 787 plane caught fire, while an All Nippon Airways flight was forced to make an emergency landing because of a battery malfunction.
The issues have resulted in the entire fleet of Boeing 787s being grounded.
Boeing, which has orders for more than 800 Dreamliners and competes against Europe's Airbus, has halted deliveries of 787s.
The incidents prompted authorities both in the US and Japan to launch inquiries to try to find out what caused the battery problems.
However, earlier this week, Japan's transport ministry said that safety inspectors had found no faults with the battery, leading to concerns that the planes might remain grounded for a while.
Some analysts have warned that Boeing may even have to go in for a major redesign if the problems are not related to the battery.
The fear is that any such move could end up being a lengthy one, depending on how serious the problem is, and may also require the 787 to go through a fresh airworthiness certification process.
After the incidents involving the JAL and All Nippon Airways planes, the US Federal Aviation Administration (FAA) said both the batteries had leaked electrolyte fluid and there had been smoke damage to parts of the aircraft.
The FAA has said that the airlines must demonstrate battery safety before flights can resume.