Shure Dual Wireless Microphone System GLXD4Key Features and Specifications: Automatic Frequency Management: Uses LINKFREQ to scan, identify, and switch to the best open frequencies without audio interruption. Integrated Battery Charger: The receiver features a built in port to charge Shure SB902 lithium ion batteries, allowing for charging during use. Battery Status Display: High resolution LCD screen displays battery life in hours and minutes. Operating Range: Typically up to 100 feet (30 m)