WASHINGTON ( TheStreet) -- Boeing ( BA) and the Federal Aviation Administration said they have learned from their mistakes regarding certification of the 787 Dreamliner. The mistakes led the FAA to ground the much-heralded new aircraft for three months, ended May 20, after two January incidents involving overheated batteries on 787s operated by Japan Airlines and All Nippon Airways. Since then, "We advanced the state of the art for testing lithium ion batteries," Mike Sinnett, Boeing's chief engineer for the 787 program, said Wednesday at a hearing of the aviation subcommittee of the House Transportation Committee. The hearing was titled "Lessons Learned from the Boeing 787 Incidents." "We pushed the state of the art so we could cause a battery to fail in a similar way to the way it failed on the airplane," Sinnett said. The JAL and ANA incidents both occurred, he said, because of short circuits inside the airplanes' batteries. The batteries include a "burst disk" that acts as a safety vent. In response to the incidents, Boeing needed to devise a method to create excessive energy in the battery cell without overcharging it, which would have led to a different type of failure. Boeing was able to heat a battery cell by wrapping it with a heating element, releasing enough heat to cause other cells in the same battery to vent as well. "Now we can replicate a cell failure with sufficient energy to cause that venting," Sinnett said. While Boeing has been able to protect against battery fires by wrapping the batteries in a steel case, it has not yet determined the root cause of the fires in the Japanese airlines' two aircraft. A study by the National Transportation Safety Board is ongoing. As for the FAA, "We now have a much more robust process for testing lithium ion batteries if they're used in aviation," Peggy Gilligan, FAA associate administrator for aviation safety, told the subcommittee. "That's a very important lesson and that's already in place." One improvement is that the FAA expects more accountability by contractors in the supply chain, she said. Additionally, Gilligan said, other industries had developed expertise in lithium batteries and now the FAA is predisposed to consult such experts. "Some of these new technologies are not just used in aviation," she said. "Boeing brought together a number of experts on lithium batteries and we learned a great deal from them. So if there is a community of experts outside of aviation, (we will make sure) we know how to reach them."