Is your laptop an airborne fire risk?

Under CASA's guide for dangerous goods (PDF), it recommends carrying all permitted lithium batteries in carry-on baggage. Additionally, passengers that choose to bring spare HP NY220AA battery can only bring up to two of them, must place them in carry-on baggage and must protect them from short circuiting. Acceptable means of doing so include placing them in 12 Cell Acer Aspire One Battery separate plastic bags or in their original packaging to insulate the batteries' terminals.
For most travellers, this shouldn't pose a problem. Presumably, the spare batteries are for flights where passengers would want to keep their batteries in their carry-on luggage. However, there are also limits on the capacity of batteries that are permitted.
Batteries that are rated up to 100Wh are permitted under the UM09H36 conditions mentioned before, but if they are rated at 160Wh or above, they are not permitted at all. Between this, batteries that are rated above 100Wh and below 160Wh must be approved by the carrier to be permitted on-board, according to CASA.
While the majority of devices on the UM09H41 market fall safely below the 100Wh mark, a couple of higher-spec laptops approach the Acer Aspire One 533 Battery edge of these limits. Dell, for example, has 9-cell batteries for some of its laptops. These batteries are rated at 85Wh. The 17-inch MacBook Pro comes even closer to the limit with its 95Wh battery.
Where safety concerns start to come into play are when passengers purchase external Acer Aspire One AO533 Battery packs. ZDNet Australia had a quick search, finding several external Acer Aspire One 532h Battery packs that were over the 100Wh limit. For example, the PowerPad 130 by Electrovaya, and the HyperJuice MBP-150 by Sanho.
One product in particular was rated at 222Wh the Sanho HyperJuice MBP-222 strictly forbidden for carriage by CASA.

Is it really dangerous?
The US Federal Aviation Authority (FAA) also issued a safety alert (PDF) after an event last year where a

Acer Aspire One 533 battery United Parcel Service cargo plane carrying a large quantity of lithium batteries caught fire after take-off and crashed, killing the crew.
In the alert, it said that the explosive potential of ACER UM09H31 Battery lithium batteries could damage and easily perforate cargo liners, reducing the effectiveness of the ACER UM09H36 Battery aircraft's fire suppression measures. It also said that the suppression agent used on the flight, Halon 1301, is ineffective in controlling fires caused by lithium batteries.
It also doesn't help that it was recently discovered that Apple's laptop batteries can be hacked and theoretically used to start a fire. In Acer UM09H41 Battery extreme circumstances, it might be possible for a malicious hacker to install malware on the laptop and set it to trigger the battery during the victim's flight.
With that in mind, it seems sensible enough to limit risks by placing limits on Acer Aspire One 532h Battery capacity. However, barring intentional misuse, passengers shouldn't be overly concerned that their fellow flight-mate's laptop is about to explode. The FAA, which oversees significantly more flights than CASA, saw just two instances of lithium GATEWAY M320 Battery incidents last year (PDF), both of which occurred in the airport terminal. In addition, there were just 118 instances involving any type of battery in the past 10 years, including cargo planes.