As I have read, lithium batteries can provide extremely high currents and can discharge very rapidly when short-circuited. Although this is useful in applications where high currents are required, a too-rapid discharge of a lithium battery can result in overheating of the battery, rupture, and even explosion. Lithium-thionyl chloride batteries are particularly susceptible to this type of discharge. Consumer batteries usually incorporate over current or thermal protection or vents in order to prevent explosion.
Because of the above risks, shipping and carriage of lithium batteries is restricted in some situations, particularly transport of lithium batteries by air.
Australia Post prohibited transport of lithium batteries in air mail during 2010.
UK regulations for the transport of lithium batteries were amended by the National Chemical Emergency Centre in 2009.
In late 2009, at least some postal administrations restricted airmail shipping (including EMS) of lithium batteries, lithium-ion batteries and products containing these (such as laptops and cell phones). Among these countries are Hong Kong, USA, and Japan.
Hope this helps!