Design background: In the past years, some of our customers asked if we could design a machine with back light, with two independent channels and other features in this small size super thin control unit. So this model is especially designed for those people who suffer different pain in different area, has to use more than two machines, now two machines in one, you do not need to operate two machines like the chiropractor does in the clinic. Now it can save 50% time when two different level of pain in different areas of body are treated at the same time. This incredible device is applying the modern electronic simulation technology to improve the micro circulation of the human body, promote the absorption of inflammatory substances, relieve the tissue adhesion, and alleviate pain; Included in this package: 1 Pro8AB upgrade version device, 2 Pairs of snap-on adhesive electrode pads 2 1/2 inches, 2 Electrode leads, 1 USB extension wire, charging from computer, 1 AC adapter (100-240V), charging from wall outlet, 1 Pads sticking and wire rewinding holder, 1 Placement point chart, 1 Instruction manual, 1 Free illustrated educational reference booklet, 1 lifetime warranty card. If any questions, please feel free to contact us. —NO WORRY about those traditional TENS units which are powered by AAA or AA batteries any more as our TENS units are powered by rechargeable ion lithium battery which keeps continuous working for about 8-10 hours. —Please read reviews for comparison with features, functions and long term benefit.