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Boeing had numerous reliability issues with the main batteries on its 787 Dreamliner long before the two battery incidents this month grounded the entire fleet.

More than 100 of the lithium-ion batteries have failed and had to be returned to the Japanese manufacturer, according to a person inside the 787 program with direct knowledge.

“We have had at least 100, possibly approaching 150, bad batteries so far,” the person said. “It’s common.”

The frequency of battery failures reflects issues with the design of the electrical system around the battery, said the person on the 787 program.

Most of the batteries were returned because they had run down so far that a low-voltage cutout was activated.

At that stage, the batteries, which cost about $16,000 each, are essentially dead and cannot be recharged.

The failures likely occurred on planes flown by Boeing and on those delivered to its customers.

For airline operators, such failures could be costly in terms of airplane downtime and inconvenience.

These problems seem separate from the two more significant incidents, when a battery caught fire on the ground in Boston and another smoldered in midair in Japan, forcing an emergency landing.

But the electrical system that monitors and controls the batteries is under scrutiny by the National Transportation Safety Board and other safety investigators as they probe the cause of the recent incidents.

Boeing spokeswoman Lori Gunter declined to confirm the number of battery problems encountered on the 787 program.

However, she acknowledged that there has been a series of problems and listed “the top three reasons for Boeing returning batteries” as batteries running down, being improperly disconnected, or exceeding their expiration date.

A battery that’s left on with no other power source, Gunter said, “will deep discharge (and) cannot be recharged or reused.”

And one that’s improperly disconnected, she added, “trips one of the protection features and renders the battery unusable.”

On Tuesday evening, The New York Times reported that officials of All Nippon Airways (ANA), the 787’s biggest operator, said in an interview that the airline had replaced 10 of the batteries in the months before the two battery incidents that grounded the jets this month.

Between May and December last year, The New York Times reported, five of the 10 replaced ANA batteries were unexpectedly low in charge, three failed to start normally, one showed an error reading, and another “failed.”

The person on the 787 program with knowledge of the problems said that the electrical-system design makes it commonplace for airline mechanics to inadvertently run the lithium-ion batteries down too low.

Because lithium-ion batteries can be dangerously volatile if undercharged, as well as when overcharged, an automatic cutoff is built into the 787 batteries so that if the charge falls below 15 percent of full, the battery locks.

“It latches — locked out — and we cannot override that,” the person said.

In that case, it can only be sent back to the manufacturer, GS Yuasa of Japan.

The design of the 787’s electrical system includes a battery switch in the cockpit. But even when that main switch is off, the battery comes on when certain ground tasks are performed.

Just as a car’s dome light will come on even when the ignition is off, drawing power from the battery, so too on an airplane certain maintenance tasks will bring the battery to life.

For example, if an airline mechanic puts jet fuel in the wing gas tank when the airplane is otherwise dark, as soon as the fuel door opens the battery will begin to provide power for the gauges that measure the fuel level.

If that door latch is not properly closed or if the mechanic encounters a problem or leaves something else open too long, the 787 battery can drain down below the critical 15 percent level in an hour, the person said.

The 787 batteries are unique and the system supplier, Thales of France, insists that the original manufacturer — its subcontractor GS Yuasa — must be the sole supplier.

So all the dead 787 batteries have been shipped back to Japan and replacements have had to be sent from there.

Dominic Gates: (206) 464-2963 or