Review on AQQA Aquarium Lithium Battery Air Pump - Multifunctional, Rechargeable, Energy-Saving, and Quiet Oxygen Pump with One/Dual Outlets, Air Stone, and 2600mAh Battery - Suitable for Indoors, Power Outages, and Fishing by Barbara Goodwin

Amazingly quiet! I was definitely surprised. The LEDs for battery level etc are VERY BRIGHT and I actually taped them on to prevent my fish from waking up at night due to the light. (And then covered the unit with a cloth.) I only use one of the two air vents, but I haven't had any notable problems with airflow. This device doesn't have an air volume control, but I have an air stone that I can use to regulate the air flow. You can turn it on and off periodically to save battery. I noticed that if there is a power outage, the setting reverts to the original "always on" setting. You may need to manually set the interval during a power outage if you want longer battery life. We've only had power outages so far, so I can't confirm that. The power switch toggles the air parameters. Electricity (with battery backup), interval air (with battery backup), battery. etc. I have not yet tested how long this device lasts on battery alone. I have to do this soon. I'm thinking about buying another one of these as I'm not sure if I got the blackout battery pack D for another tank.