Grace Digital GDI-AQRCK400 Dual Powered Wireless Rock Speaker with Built-In Rechargeable Batteries and Dual Powered Transmitter (Discontinued by Manufacturer) 150-Feet range Transmitter is AC or battery powered. Includes built-in rechargeable battery Connects to stereo, TV, iPod or any MP3 player Expandable up to 10 additional accessory speakers can be added 900 MHz wireless technology for up to 150' foot range to listen to your stereo, iPod, or TV outside in your yard or on your patio The high performance wireless rock speaker has a built in rechargeable battery for up to 7 hours of one charge. Or plug them into AC power for maximum play time. The transmitter works on the included AC power adapter or optional AA batteries. Control the volume and power directly on the rock speaker or by adjusting the music source's volume level Connect the family of Grace wireless speakers to the Rock's main transmitter