Perversely, according to Wikipedia, lithium-ion batteries containing more than 25 grams (0.88 oz) equivalent lithium content (ELC) are forbidden in air travel.
Passengers are not allowed to carry more than a certain concentration in their carry-on baggage and only in checked baggage if it is in its original packing – i.e. largely discharged.
Apparently this restriction is due to the possibility of batteries short-circuiting and causing a fire, yet the FAA gave approval for Boeing to use the technology as the primary electrical store on the 787 in far higher densities than passengers are allowed.
The Dreamliner is the first plane in the world to use the lithium-ion batteries, which are lighter, hold more power and recharge more quickly, but have been known for years to be prone to overheating and even catching fire under a variety of conditions including over-charging, shock and short-circuiting.
Technologies do appear to exist that greatly reduce the volatility of the lithium-ion battery and, of course, the use of nickel cadmium is always an option, although it has a weight implication as larger battery packs are required to achieve the same storage. Not only that, but changes to the re-charging, monitoring and control systems would be required, which cumulatively make a move to NiCd very costly both for Boeing and the airlines operating the 787.
The problem will get solved, but judging by some of the blog traffic out there, many from an engineering background are questioning the use of these batteries in the first place – and what is viewed by some as the too-close relationship between the aircraft maker and the FAA leading to a less than 100% satisfactory solution from a safety point of view.