It is application by centrifugal force & inertia like a gyroscope. There is no any battery or electricity inside the device, it is powered by rotating the wrist

Functions:

• Perfect exercise gadget for sports like golf, tennis, squash, cricket, badminton, baseball, bowling, basket-ball, motocross, mountain climbing.
• Increase strength in fingers, wrists, hands, forearms, biceps, triceps, ligament and shoulders.
• Great benefit for musicians, guitarists, pianists, drummers.
• Rehabilitates sore muscles and joints.

Features:

• Brand new & high quality!
• New designed sports apparatus.
• Exercises arm, wrist and removes fatigue.
• Promotes blood circulation.
• Based on mechanical principal.
• Rotating speed can reach 8000 rev/min.
• Built-in LED flashlight (batteries built-in).
• LED automatically lights up while spinning.
• For people 6 years and older.
• The easy yet effective exercise to improve your forearm, wrist, finger strength.
• Power up your shots, strikes & take your games into next level.
• Prevent injury, sore wrist and tennis elbow (Lateral Epicondyle ) or even get rid of it.
• Great for fitness, rehabilitation (Therapeutic) or just for fun.
• It's a very nice gift, especially for sport lovers and musicians.

Specification:

• Material: Zinc alloy rotor + PC plastic shell
• Colors: Blue
• Product dimensions (Dia. x H): 7.5 x 6.5cm
• Gross Weight: 290g

Package Includes: 1 x Gyroscope power ball 1 x Starting rope 1 x Hand strap 1 x Manual