TOKYO — As Boeing’s 787 Dreamliner returns to the skies, Japanese pilots are nervous about whether they would receive enough warning about any hazards with the jetliner’s new battery system.

Toshikazu Nagasawa, the director at the Air Line Pilots’ Association of Japan, said on Tuesday that some pilots remained concerned about the changes Boeing made to the 787’s lithium-ion batteries after two incidents involving smoke or fire led to the grounding of the fleet early this year.

Mr. Nagasawa said the pilots were also dismayed that Boeing did not adjust its cockpit displays to provide more substantial alerts if the batteries started to overheat.

Boeing officials acknowledged in interviews that they had not expanded the alerts. But they said the new battery system virtually eliminated the chance of fire or any risk to the plane. Safety regulators in the United States and Japan, and the eight airlines flying the jets, have signed off on the changes.