NTSB performing chemical tests on defective 787 'Dreamliner' battery

"Detailed examinations will be looking for signs of in-service damage and manufacturing defects," the NTSB update continued. "The test program will include mechanical and electrical tests to determine the performance of the battery, and to uncover signs of any degradation in expected performance."

The NTSB said the 787's manufacturer, Boeing, has been "providing pertinent fleet information, which will help investigators understand the operating history of lithium-ion batteries on those airplanes."

The agency said last week that the batteries on a 787 that caught fire exhibited signs of accelerated temperature increases known as "thermal runaway" and short circuiting.

Thermal runaway is a scientific term for a situation in which a temperature increase in a device spurs other temperature increases, which leads to a uncontrollable cycle that could end in an explosion.

The NTSB has said that it will not play a role in determining when the 787 will be cleared to return to flight. The agency has said it is only investigating the circumstances of the Boston incident to determine what caused the electrical fire that was sparked by the 787's battery defect.

The NTSB has said that it is providing information to the FAA's concurrent 787 review, for which Department of Transportation officials have not given a time frame. DOT officials have said only their review will be "comprehensive," and that the 787 will not be cleared to fly until concerns about the safety of its batteries are completely addressed.