It's not going to work in a full blackout. It will give you a few minutes to shut off the tv/ provide steady power in brownouts or brief power outs so your set isn't hit by constant voltage jumps/cycling on and off. If you want one that will give you some serious blackout usage, you'd need to get one of the 1000W/2000W ones like those crazy things I listed. I know some people who have them. They're cool I guess so you can watch TV when the power's out, but they're expensive and batteries eventually need to be replaced. Not trying to sound negative since this will pretty much be standard fare for most battery backups that are affordable, just trying to make sure you've got a good sense of expectation for what it can/can't do.
Also you probably want to keep the TV separate from other appliances you don't really care about. The more things you have on, the less time you'll get on the battery. If you have too much plugged in, you won't get any time and it'll just switch off because you'll burn through the juice immediately so be mindful the wattage it's rated for and how much you plug in. Typically, the "standard time" they're rated for is for 1/2 wattage load. Some also have a rating for full-load battery life. Try to hook nonessential things to other surge protectors etc...
