We rush and accidentally leave small things out like chargers. And then, our pets get to them. Sometimes, we just seem to misplace our things and can’t quite put our finger on where it is at. Or you may travel a lot and just need a spare with you for the “just in case.” This charger is an AC wall plug ONLY and DOES NOT include a USB cable. It is meant to be used on InTENSity units that are the 2nd generation such as: InTENSity 12 TENS Unit, InTENSity Twin Stim IV TENS & EMS Combo Unit, InTENSity IF Combo II TENS & Interferential Unit, InTENSity Select Combo II TENS, EMS, IF, & Russian Stim Combo Unit.