The Silent Air® B11 Battery Powered Air Pump is a powerful and versatile air pump that will aerate your aquarium during a power outage or when there is any interruption to your AC power. A must for any aquarium, the Silent Air® assures continuous aeration of your tank giving you peace of mind and keeping your fish safe. This air pump provides your tank with needed air whenever the AC power is interupted. Simply connect your Silent Air® pump to your air line or aerating stone, insert two "D" size batteries (not included), plug into any AC outlet and turn the on/off switch to the ON position. The Silent Air® will now continuously monitor your AC power to detect any interuption and will turn on automatically as needed providing your fish with life-saving aeration during a power-outage. Designed for extended operation, the Silent Air® B11 uses two large "D" size batteries that insures hours of continuous operation. The Silent Air® provides enough air for most aquariums up to 55 gallons in size and can also be used for transporting fish or for use in temporary tanks while cleaning your aquarium. Whether you have a tripped breaker, a blown fuse or complete power outage, the Silent Air® B11 Battery Powered Air Pump will give you hours of needed air when you need it most. It is recommended that you test your Silent Air® periodically 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. Measures 5.5"Hx 3"Wx 2"D and has a 5' power cord for easy placement.