Boeing Co. said Friday that safety upgrades to the 787 Dreamliner's battery systems may allow commercial flights to restart within weeks, ending a two-month grounding of the composite-plastic fleet.

Changes include installing a new enclosure for the battery, a focus of regulatory probes after a fire on one aircraft and smoke on another, and adjusting the charger, Boeing said in Tokyo. The device will also undergo more rigorous tests, Boeing Commercial Airplanes president Ray Conner said. The improvements will allow the resumption of service once the Federal Aviation Administration signs off, and Air India may lead the way, returning its five jets to flight as soon as April. Boeing would also be able to restart deliveries of the aircraft, for which it has a backlog of more than 800.

"It is reasonable to expect that we could be back up and going in weeks, not in months," Mike Sinnett, vice president and chief project engineer of the 787 program, told reporters in Tokyo. "We understand the work to be done, and we've got a fairly good notion of how long it will take."

Regulators led by the FAA ordered the global fleet of 49 Dreamliners parked on Jan. 16, forcing the eight carriers operating the plane to shuffle their schedules and put other jets into service to fill the gaps.

Air India's 787s will start receiving the Boeing modifications next week, and the state-owned airline's planes may be back in service in April. LOT Polish Airlines, which flies two 787s, expects to be among the first carriers to resume flights with them.

United Continental Holdings Inc., whose six Dreamliners are the only ones in service at a U.S. carrier, has not changed plans to keep them off its schedule through June 5, with the exception of a Denver-Tokyo flight slated to start in mid-May.

Boeing will be allowed "limited test flights" with two 787s that will have prototype components of the new battery system, the FAA said Tuesday.