This passive volume control works without a battery. It does not boost the volume, but it allows you to turn the pickup signal down.
It functions best when the input impedance of the device you plug your guitar into is 1 Mega Ohm (preamp/amp or mixing board-channel). If this input impedance deviates by a large amount (i.e. 100 Kilo Ohms or 10 Mega Ohms), you may experience diminished range (from "full volume" to "off" within a 1/3rd rotation) or, in extreme cases, a slight hum when the potentiometer is at middle position. This is a normal phenomenon when passive potentiometers are used with piezo based pickups. At "full-on" or "full-off" it will always be noise-free. A lot of customers use the Volume Control like an extended on/off switch.
