That's what I use. It works nicely I have it hooked up to my protien skimmer It works but the most I have let it go was about 30 mins.
I also have this APC UPS Hooked up next to my tank with nothing to it so in case of a power outage I can un plug an mj1200 from my wavemaker and put it directly onto the UPS
I've been using a 750va with 1 extra battery on a single Tunze, when power goes out it drops to it's slowest setting; longest it ran for was 22 hours. I got the unit with no batteries off eBay and picked up new batteries.