Dummy batteries are not required in 18 volts instruments when the batteries contactors can be connected.Content of the pack : * 1 ZAM box * One 24 volt AC power supply unit. * 1 high quality 10 feet jack-jack cable, Senn® or Cordial®. * 2 dummy batteries in 9 volts Additional Information Compatibility For pre-amped guitars and basses equipped with a 9v battery and a stereo jack.