The WL-T wireless transmitter is compatible with the WL series wireless systems and the wireless Katana-Air guitar amplifier. It can be used as a backup in case your original transmitter is lost or damaged. When pre-charged, the WL-T can also serve as a backup transmitter for live performances if needed. To charge the built-in battery and establish a connection with your BOSS wireless receiver, simply repeat the same steps as with your original transmitter. Note: As a standalone device, the WL-T has no audio functions. A compatible wireless receiver is absolutely required.