Backup Power Supply Size Question

I have a quick question about back up power supply sizes that hopefully someone here can answer.

I decided to try out Vonage's phone service. They have a special right now where they give you the router and the first 2 months free. Called last Friday and got the equipment last night. Took all of 5 min to set up and get running. I was thinking of putting this equipment on a back-ups to make sure it still worked during a power outage.

Here's what needs supported. A Motorola cable modem, a Microsoft MN-700 wireless g router, and the Linksys RT31P2 router that Vonage sent. I was already using the Microsoft router and it works perfectly when I plugged the Linksys router into it. For some reason the Microsoft router didn't like being plugged into Linksys router. Claimed it couldn't see the cable modem.

All three devices run off of a brick that says 12 VDC 1A. They can't be using more than 100 watts between the 3 of them. I was just wondering what size of a backup would be needed to get 30 - 60 min of power supplied to these 3 devices? Any longer than that and I'll have bigger problems than a dead phone line.

dbates, i found this. Hope it is compatible.

Hefty power - up to 200amps! With the simple addition of your deep cycle or automotive battery, the PowerSafe provides everything you need for a 12V, 75 to 200 amp, uninterrupted power supply. At home or in the field, in daily use, as well as during emergencies, this clean, portable unit will keep your equipment fully powered with ample capacity. We offer three DC models designed for light, medium or heavy use. All models come with a heavy duty, vented battery enclosure suitable for use in the home or office, triple port automotive cigarette outlets for DC use, and fully automatic AC chargers. It's compact dimensions: 18" x 10.5" x 9.5" make it easy to store or transport.

Link

Sanc'.