Battery-powered air pumps can be very cost effect ways for providing aeration and water current to your tanks. I happen to have the Penn-Plax "Silent Air" Model B11 which uses two D batteries. It can typically be purchased for about $11-15 on-line. This unit has a very useful feature: it will not turn on until it detects the AC power has gone out. If youre expecting a storm in the night or perhaps expecting a storm and you have to leave the house for some reason, it is very easy to add one or two of these to your tank. If the power does not go out they never turn on. But if it does go out and you are not around, they will buy you some time until you can get your plan in place. I would suggest using a minimum of at least one unit for every 2 feet of tank length for most standard tank sizes.
When using battery-powered air pumps (or even normal AC air pumps on a UPS unit) dont use an air stone or wood block. Simply run the tubing to the bottom of the tank. Rigid airline tubing works best but standard airline can be used. In either case you may need to add weight to the hose to keep it in place. I use a rubber band to attach the hose to my cleaning magnets and drag the magnet to place it where needed. The large rolling air bubbles will create surprisingly good current and water surface agitation for gas exchange. Ive found large rolling bubbles to be much more effective than the fine mist of bubbles produced by stones or wood blocks.
The Penn-Plax "Silent Air" Model B11 unit that I have uses two D size batteries. The unit will also run on a single battery but will obviously not run as long. In my tests running the unit on two D batteries the Model B11 unit last just short of 5 days of continuous use. I was very impressed with this. A unit like this is a must-have for every person with an aquarium.
This is taken from "Disaster Readiness" by Richard Durso, published in Advanced Aquarist, August 2002.