Most acoustic/electric guitars have an on-board Preamp powered by a battery, or batteries, that allows you to control the guitar’s volume and EQ settings.
After-market pickup systems that are considered “active,” will also have batteries.
Plugging in a guitar cable, including the ToneWoodAmp patch cable, to the guitar, turns on the Preamp and uses battery power. It is important that when you are done using the ToneWoodAmp you unplug the patch cable to avoid draining the battery.
It is important to also set the pickup signal INTO the ToneWoodAmp. Keeping all EQ levels flat and Preamp volume at 50% is recommended.