A rechargeable battery pack that powers the system contains 8 AA nickel cadmium batteries and is connected to the stimulator/control unit with a power cable. A built-in low battery alarm indicates when recharging is necessary by sounding an intermittent beep. A normal charge, dependent on type of stimulator used (4 or 6-channel system) and intensity levels employed allows approximately 75 to 120 minutes of use. A green “ON” and a red “CHARGE” LED indicator are located on the top face of the unit (see lower photo). With the proper voltage charger, the battery pack works at either 110V AC or 240V DC environments.