I am similarly confused. I spend a lot of time in Baja, so often play in locations with iffy solar, or no power at all. I use a battery powered Bose S-1 amp, but am forced to power pedals by battery. So...to Harmony Singer 2: 4 AA batteries (4 X 1.5v = 6v), so why does the pedal say 9v power source or 4-AA batteries? Thats 9v or 6v! I don't get it. I have several pedalboards with pedals securely Velcro's down. Big pain to pry up Harmony Singer 2, undo the screw to open the back and fiddle with 4 AA batts. Can I just use a simple external 9v batt with terminal clip and center neg plug in to pedal?