SEATTLE (REUTERS) - Boeing plans to conduct two flight tests of its revamped 787 battery system, possibly as soon as the end of the week, according to three sources familiar with the matter.

The 787 flights, the first since last month, would mark another step toward Boeing's recently announced goal of returning the grounded jet to service in a matter of weeks, not months.

Regulators banned the plane from the skies in January after lithium-ion batteries burned on two 787s in quick succession that month. The Federal Aviation Administration (FAA) gave Boeing permission for a single "ferry" flight on Feb 7 to move a jet to Washington state from Texas, carrying minimal crew and no passengers.

The FAA on March 12 approved Boeing's plan to test a redesigned battery system, to prove it is safe. The plan includes a rigorous battery testing standard Boeing helped develop but did not previously use. Boeing said last week that it was one-third of the way through the testing, and expected to finish in a week or two.

Boeing's prediction drew scepticism from some regulators and industry experts, who said it was too early to say when the Dreamliner would fly again with the root cause of the battery overheating still unknown.

The testing regimen set by the FAA requires one flight test. However, Boeing plans to conduct two flights: One for its own purposes and a second to gather data to submit for FAA approval, according to the sources, who spoke on condition that they not be named.

The flights could still be delayed by weather or other factors. Flight plans for the events had not yet been filed with the FAA.

The flights would depart from and return to Paine Field, an airport adjacent to the factory in Everett, Washington, where the 787 Dreamliner is made.