Tens Unit Machine Device Muscle Stimulator Electrotherapy Machine Rechargeable With SlipperNew Technology Multiple preprogrammed 24 different massage modes. Adjustable 20 to 60 minutes timer by using the " T " button. Rechargeable internal lithium battery. Up to 20 hours continues use. MedTens Tens Machine can be connected to a wall charger, power bank, or laptop USB port to charge. The battery level indicator reminds you to charge timely. A B Output will allow you to use it as 2 separate users. You can set separate intensities for each