Boeing officials said Friday that safety upgrades to the 787 Dreamliner's battery system may allow commercial flights to restart within weeks, ending a two-month grounding of the new aircraft.Changes include installing a new enclosure for the battery -- a focus of regulatory investigations after a fire on one aircraft and smoking on another -- and adjusting the charger, Boeing said in Tokyo.The device will also undergo more rigorous tests, said Ray Conner, the company's commercial airplanes president.The improvements will allow service to resume 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 could also restart deliveries of the aircraft, cutting into 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, and if we miss, it will be by a little, not by a lot."Regulators led by the FAA ordered the global fleet of 49 Dreamliners parked Jan. 16, forcing 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, said Arun Mishra, the country's aviation regulator.LOT Polish Airlines, which flies two 787s, expects to be among the first carriers to resume flights, according to a company statement. The Warsaw-based carrier said Boeing has agreed that advance payments for 787 deliveries slated for next year will be delayed.United Continental Holdings, whose six Dreamliners are the only ones in service at a U.S. carrier, hasn't changed plans to keep them off its schedule through June 5, except for a Denver-Tokyo flight that starts in May.U.S. regulators cleared the proposed redesign of the system this week.Boeing will be allowed "limited test flights" with two 787s that have prototype components of the new battery system, the FAA said. It must prove in flight and laboratory tests that the design meets U.S. standards, and the FAA could insist on more changes, the agency said in a statement.Resumption of flights will depend on testing and certification, Sinnett said. About 25 percent of Boeing's testing is already under way or has been completed, and 75 percent of the test plans have been approved, he said.Testing should be finished "within the next week or two," said Ron Hinderberger, vice president of 787-8 engineering.