Auto/on Battery Air Pump This pump plugs into the wall to detect if the electricity is on. If the electricity goes off, the pump turn itself on. Can be used with lift tube to increase circulation. Batteries lasted me the full 8hrs it took me to move the tank a few weeks ago. I'm sure it would have lasted much longer. I didn't want to waste the batteries to see how long it would run. Those 8 hrs was ample enough time to get your generator going in case it was a real power outage. Cost me $16 at LFS. Can be purchase online. Pro's Batter powered Light weight Portable Has on/off switch Con's Short power cord Can't pump into deep tank Must check batteries regularly to endure they work and are not damaged form moisture. 90 day warranty so you must test the unit right away This is the article that tipped me on the device. http://www.advancedaquarist.com/issues/aug2002/feature.htm
i have one but have not had the luck in battery life you described. mine lasted about 4 hours. maybe it was generic batteries . all the way around i wouldnt think of not having one in an emergency situation.