The Penn Plax Air-Pod Battery Back-Up Air Pump is an excellent reserve unit designed for use in the event of a power outage. It is also a terrific aerator for transporting fish. The Air-Pod automatically switches from AC to battery when a power failure is detected. It features an adjustable flow control that regulates its dual outlets, and a handy power indicator light that displays the active power source. Relies on four "D" cell batteries (sold separately) which provide up to 150 hours of continuous use. Impact-resistant design.