Please note: This device cannot be charged! It requires a 5V/2A power source to function properly! Important notice! Important notice! Important notice! Power supply: This device must be connected to a 5V/2A power source via a USB cable to operate properly! Do not charge! It is recommended to use a 5V/2A power source. Size selection: Before choosing, please measure the length and width of your hand. If your fingers are wide, it is recommended to increase the actual size by one centimeter. Usage guide: If you feel stiffness in your hands, it is recommended to perform a 5-minute massage and stretching before doing any strength training. Recommended training frequency: It is recommended to exercise 2-3 times a day, for a duration of 15 to 30 minutes each time