Boeing's stock has dropped only 3.4 percent, to $75.04 a share, in the two weeks since the battery fire on a 787 parked at Logan International Airport in Boston. The Federal Aviation Administration grounded the jets after another 787 made an emergency landing in Japan on Wednesday because of a smoke alarm in the cockpit. The F.A.A.'s order applied to six United jets; an additional 44 around the world have also been grounded.
(Read More: The Ties that Bind: Boeing Unlikely to Suffer Japan Fallout Over 787 Woes)
David E. Strauss, an analyst at UBS, said big investors were "cautiously optimistic" that the batteries just came from a bad manufacturing batch or could be fixed with minor changes.
But, he said, "if the F.A.A. came out tomorrow and said to redesign the battery, and Boeing said it would take three months, the stock is going to go down on that."
"Investors have been expecting that Boeing would finally start freeing itself of the cash drain from all the problems in developing the plane and that they would start to see more rewards now," he added.
The National Transportation Safety Board said Sunday that it had ruled out excessive voltage as the cause of the battery fire on the 787 in Boston, adding to the mystery of the cause.
Besides the hazards to passengers if fire or smoke escaped from the battery containers, the problems are important because the 787 relies more on electrical systems than previous planes. Its use of electric rather than hydraulic systems is one of the innovations, along with more efficient engines and a lightweight carbon-composite structure, enabling the plane to save on fuel.
Boeing officials have said they had not previously had any problems with the batteries during 1.3 million hours of flights by their test pilots and eight airlines. Marc R. Birtel, a Boeing spokesman, said Saturday that one lithium-ion battery caught fire in 2006 during tests that Boeing held with the F.A.A. But he said the problems stemmed from the way the test was set up, and not from the battery design.
Depending on its agreements with each airline, Boeing was probably spending several hundred thousand dollars to $1.5 million a day to compensate carriers for lost passenger traffic or the need to lease other jets to maintain service, analysts said. Those penalties might be paid as a mix of cash and discounts on future plane purchases.
Boeing also plans to keep building 787s, at its current rate of five a month, to keep its supply chain intact. Mr. Strauss, the UBS analyst, estimated that the company spent $175 million to $225 million on each plane, so that would tie up more cash if it took time to fix the problems.
And the costs would mount even more rapidly if the planes remained grounded for several months or significant design changes were needed. That could slow Boeing's plans to increase production to seven jets a month in mid-2013 and 10 a month by the end of the year.
Still, Boeing, which also has a giant military business, has about $11 billion in cash, and it cannot build some of its other planes, like the 737 and the 777, fast enough to keep up with the demand.
The 737 and 777 programs "are printing money," said Richard L. Aboulafia, an aviation analyst at the Teal Group in Fairfax, Va.
"This is why small, niche companies don't build large commercial jets," he said. "You need multiple product lines to insulate yourself from problems."
One risk for Boeing is that adjustments in the lithium-ion batteries could require changes in other electrical equipment. But the biggest risk is that the batteries could prove too volatile, and Boeing would have to redesign its systems to use heavier and less-efficient nickel-cadmium batteries.
Some technical experts doubted that such a drastic change would be needed. But smaller lithium-ion batteries have caused fires in cellphones and laptops in the past. Cessna was forced to replace lithium-ion batteries on its CJ4 business jet with nickel-cadmium after a battery fire on the plane in 2011.
Airbus is using lithium-ion batteries in its new A350 XWB jet, which is scheduled to enter service in 2014. But Airbus said the batteries in its plane, which will compete with the 787 for sales, were smaller than Boeing's and carried lower voltages, making them less vulnerable to problems.
The F.A.A. set a series of conditions in 2007 to ensure that the 787's batteries did not overheat or spew flammable materials. It was reviewing whether the company had properly taken those steps.
"Until they can replicate what happened, people won't feel 100 percent confident," said Howard A. Rubel, an analyst at Jefferies & Company. "You know they have to replicate it."