UPS battery backup question

[Coasting]

So i have a question i hope you guys can answer.

Best buy has a few ups backups on sale and i wouldnt mind getting one.
Murphys law.... knowing my luck power will go out the moment everyone leaves for work and nobody will be home for.... 9 hours. We have a generator and spare battery backup we can plug stuff into. And multiple battery air pumps.

I want something I can have a single powerhead (5w) plugged into that will keep that 1 item going until people get home from work and somebody can deal with plugging stuff into other things.

Now ive looked at various brands and not all list how many watts they are, but they list the amount of energy in a surge they would protect from. But many of these are only saying they will run for 15 minutes.... enough time to save your computer documents and shut down the computer properly. And they talk about software and what not.... will these backups still work for 1 or 2, 5w hydor powerheads? Will they run them for hours? Or will they shut down in minutes even if the battery isnt drained? I guess i just dont fully understand how they actually work. Dont want to end up buying one that only works when its connected to a computer with software. I want one that keeps running my powerheads when the power goes out.

Heres a few i was looking at.

http://m.bestbuy.ca/?lang=en#/catalo...227&lang=en-CA

http://m.bestbuy.ca/?lang=en#/catalo...821&lang=en-CA

http://m.bestbuy.ca/?lang=en#/catalo...845&lang=en-CA