The Pentagon said it plans to continue using lithium-ion batteries on the new F-35 fighter jet despite problems with similar batteries that have grounded Boeing Co’s new 787 airliner and are causing Airbus to rethink their use on its A350 jet.

Joe DellaVedova, spokesman for the Pentagon’s $396 billion F-35 program office, said on Tuesday that the lithium-ion batteries used on the new radar-evading fighter were made by different manufacturers than those used on the 787, and the jet’s battery systems had been rigorously tested.

“The bottom line is the lithium-ion batteries used on the F-35s have been through extensive tests and have redundant systems to protect the aircraft and battery compartments; they are considered safe,” DellaVedova said.

DellaVedova said there had been some irregularities with the lithium-ion batteries not starting properly in cold temperatures that were being addressed, but no issues affecting flight safety had come up during years of testing.

All 50 Boeing Dreamliners in commercial service were grounded worldwide on January 16 after a series of battery-related incidents, including a fire on board a parked 787 at Boston’s Logan International Airport and an in-flight problem on another airplane in Japan.

The groundings have cost airlines tens of millions of dollars, with no solution yet in sight, and have sparked growing concerns among aerospace industry executives about whether the powerful but delicate backup energy systems are technically “mature”, or predictable.

The U.S. National Transportation Safety Board, which is examining the 787 fire in Boston, said it was looking at the total design of the Boeing 787 battery, built by Japan’s GS Yuasa Corp on behalf of France’s Thales SA, including the charging system, electrical interconnections, and their thermal isolation of different battery cells from each other.