APC Power-Saving Back-UPS ES 8 Outlet 550VA 230V
Battery Backup & Surge Protector for Electronics and Computers
EDIT: Appears to no longer be free shipping
RRP $160
Next cheapest price - Umart $115
• Adjustable voltage sensitivity
• Audible alarms
• Automatic self-test
• Battery failure notification
• Battery replacement without tools
• Battery-protected and surge-only outlets
• Cold-start capable
• Data-line Protection
• Hot-swappable batteries
• Safety-agency approved
• User-replaceable batteries
Product Page - http://www.apc.com/shop/au/en/products/APC-Power-Saving-Back-UPS-ES-8-Outlet-550VA-230V-AS-3112/P-BE550G-AZ
Runtime Graph - http://www.apc.com/products/runtimegraph/runtime_graph.cfm?base_sku=BE550G-AZ&chartSize=large
I'm guessing you won't get much time, that it more to allow you safely shut down?