The Penn Plax Silent Air B11 Battery Powered Air Pump is a powerful and versatile aquarium air pump that provides continual oxygen flow during a power outage or when there is any interruption to your AC power. Provides enough air for most aquariums up to 55 gallonsGreat for aerating temporary tanks and during power outages2 "D" batteries allow up to 48 hours of continuous use5' power cord for easy placementA must for any aquarium, the Silent Air Pump assures continuous aeration of your tank giving you peace of mind and keeping your fish safe. Whether you have a tripped breaker, a blown fuse or a complete power outage, the Silent Air B11 Battery Powered Air Pump will give you hours of needed air when you need it most. Periodically test your Silent Air B11 Pump by unplugging the AC cord with the unit ON which should activate your pump. Batteries should be tested and changed as needed. The AC power cord is for power detection only and will not charge your batteries. Requires 2 Alkaline "D" batteries (not included) that can provide full power for up to 48 hours depending on the life of your batteries. Length of operation with battery power will vary depending on the quality and age of the batteries used. Placing unit on a shock absorbing surface will minimize vibrational noise. Dimensions: 3"W x 2"D x 5. 5"H