Welcome to GuitarHeads.Net
This is a 9v to 18v Conversion Battery Clip. This no-solder setup is reversible and simply clips onto your current 9v connector allowing you to run 2 9v batteries (18v). Also wired into the circuit is a Mini SPDT Switch, that allows to you Toggle between 9v or 18v. All connections are Soldered, Taped, & Shrink Tubes for security. Doubling the amount of voltage is a common mod used in guitars with Active Electronics & Pickups (such as EMG) to add increased headroom, and also used on Effects Pedals (such as the Ibanez AD9 Delay) to enhance operation. Just make sure whatever you plan to mod can handle the extra voltage.