USB rechargeable eraser comes with a built-in 500mAh lithium-ion battery which is recharged by USB for convenience and long lasting charge. No need to change batteries. Includes a USB charging lead and 20 eraser refills, (10 large erasers 5mm & 10 extra fine eraser 2.4mm diameter). The extra fine eraser is perfect for fine hair line erasing for detailed artwork and technical drawing.The function button is designed to push on and off when required, allowing your hand to hold freely for maximum control. Suitable for left and right hand use. Erases quickly and precisely. Non abrasive with circular motor movement.