Actually there are many types of UPSs. The major categories are pure sine-wave, modulated/simulated sine wave and square wave UPSs. The pure sinewave category is pretty expensive and is required for electronic equipment which require under 2 ms power shifting difference, namely computers and other microchip based equipment. However, for a tv, you don't need a pure sine-wave, modulated sine-wave UPSs are absolutely fine, you won't even feel much difference on the screen when the UPS switches on. However, this is only for those TVs which are at about 100 or more, I think in normal 50Hz tv, there should a little flicker, not much of a problem I believe.
Then comes the square wave UPS, the most rugged kind of UPS. Used for lighting and fans. The fans also make a special kind of whee whee noise using this UPS. The modulated sine-wave UPS also makes the fans make the same noise but it is comparatively lesser, and the pure sine-wave UPS make only very little noise with the fans. The noise factor also depends upon the amount of charge which is still stored in batteries.
On another note, the batteries of UPSs are set to either 12v,24v or 48v. But all batteries available on the market are 12v, Lead Acid Batteries. So for a UPS that uses 24v you MUST have TWO batteries connected in series. Usually the batteries store upto 50 amps. A 1000W/1200 Kva UPS connected for example, at a load of 800W consumes P=VI, where V is 220v (in pakistan) then 800=220I, and I is approximately 4A, since at higher wattages, the voltage tends to reduce, e.g. 220 would become 200 (normal UPS, good UPSs voltage pretty much remains the same). For UPS, which use 12v to 220v conversion one battery also suffices but the amount of charge stored is reduced (1 battery) so the UPS provides power for a lesser amount of time.
For time conversion, do the calculations with the total power in KWHs.