“This does not tell you that Boeing’s plane is grounded until June,” he said. “It tells you that Boeing’s costs to United could be as if it’s grounded until June.”

A “superbox” to contain the battery or some other fix “might come sooner, but United is not paying” to have the jet until after June 5, he addded.

In a similar move, Poland’s national airline LOT said last week that it would not use the 787 before October and that it is seeking compensation from Boeing.

United is the only U.S. carrier currently operating the 787 and has six of the planes, worth $207 million apiece at list prices. Japan Airlines and All Nippon Airways have most of the 50 jets delivered to airlines so far.

Meanwhile, Japan’s Nikkei newspaper, citing sources, reported in its Feb. 22 morning edition that Transport Ministry investigators found deficiencies in how electrical-insulating paint was applied to a driving mechanism that opens and closes the 787’s fuel-tank valve. The ministry also found foreign matter stuck on a switch on the mechanism.

The ministry is discussing the cause and measures to prevent recurrences with the U.S. FAA and Boeing, the Nikkei report added.

In addition to the battery problem, investigators have been looking into a case in which a Japan Airlines 787 leaked fuel while taxiing to the runway for take-off at Boston’s Logan International Airport in January.