The Sennheiser SK 2000 Bodypack Transmitter Bw (626 - 698 MHz) is ideal for musicians with its wide frequency ranges and plethora of features. This sturdy transmitter uses 4 RF output powers (10, 30, 50, or 100mW) for extended transmission ranges and more channels per frequency range. The optional rechargeable batteries can be charged inside of the unit with the external charging contacts.