TOKYO - A Boeing 787 dreamliner operated by Japan Airlines Co (JAL) was grounded after discovering a battery problem during a checkup at Japan's Narita airport, reported local media Wednesday.

The checkup was carried out around 4:15 pm local time on Tuesday before the jet heading for Bangkok at 6:05 pm local time, Japan's Kyodo News quoted JAL as saying, adding cockpit displays showed signs of malfunction in the main battery and charging systems.

JAL confirmed that a venting valve for one of the eight lithium- ion battery cells had been activated.

The valve is among the modifications made to the 787 battery systems following a months-long worldwide grounding of the jet last year. It is designed to release pressure in battery cells in the event of overheating.

"Improvements to 787 battery system appear to have worked as designed," Kyodo quoted Boeing's comments on Twitter as saying.

The airline also found that battery liquid had sprayed inside the cell container.

Battery overheating incidents had triggered worldwide grounds of the Boeing's advanced jets and the company has made some improvements to the 787's battery system.