The Comfy Stim Ultra is a 4 channel, 8 electrodes, electrotherapy device that offers the user the choice of 5 modes of TENS and 3 modes of EMS you can adjust with the parameters you prefer and 24 preset fixed programs (12 TENS & 12 EMS Programs). The Comfy Stim Ultra is extremely popular with the end user and its clinical features such as a large LCD screen, 4 channels and multiple wave forms makes it a hit with the healthcare practitioner as well. Use four AA batteries or provided 9 volts power supply adapter