The warning is likely to trigger tougher international packaging standards for all such cargo.
In the past, Boeing provided similar guidance to airlines but only if they specifically requested technical advice, and it signed an industry-wide technical paper highlighting that design standards for airlines hadn't contemplated the high temperatures and explosive gases that can result when thousands of lithium batteries erupt in what is called a 'thermal runaway'.
Boeing's latest warning goes further because it was unsolicited and amounts to a formal recommendation that is likely to be followed by virtually all customers.
Conventional fire-retardant chemicals on planes are not able to put out some of the lithium battery fires, according tests conducted by the US Federal Aviation Administration. Most other kinds of batteries have not been shown to explode or burn at such high temperatures
Dozens of airlines, including Delta Air Lines, British Airways, Cathay Pacific, Singapore Airlines and Air France, have already voluntarily stopped putting bulk lithium batteries in the cargo holds of their passenger planes. Some carriers have stopped accepting cargo shipments of large numbers of lithium batteries altogether.
As of July 1 2015 as many as 28 carriers had imposed permanent or temporary bans on bulk shipments of lithium batteries as cargo on passenger planes, according to data assembled by the International Air Transport Association, the leading global airline trade group.
In addition, Airbus Group SE and a United Nations-backed panel of global safety experts also are on record about potentially catastrophic fire and explosion risks from rechargeable and non-rechargeable lithium batteries, which can reach temperatures hot enough to melt aluminium.
Boeing's formal warning indicates that the company may be willing to join the growing chorus of pilot unions, airlines and other industry players calling for a reassessment of how lithium batteries are transported as cargo on all types of commercial aircraft.