This Derwent electric rechargeable eraser comes with a built in 500mAh lithium-ion battery that is completely rechargeable with USB, and will last long enough for all your erasing needs. There is no need to change batteries, simply the moment it runs out just connect and plug in the USB connection and it will start charging right away. Inside you will find not only a USB charging cable but also 20 eraser refills (10 large erasers 5mm and 10 extra fine erasers 2.4mm diameter). For more detailed erasing of artwork or technical drawings the extra fine eraser is perfect thanks to it\'s size and precision. Located on the electric eraser is a function button that is designed to push on and off, allowing your hand to hold freely for better handling, maximum control and is perfect for both left and right hand dominant people. It will erase incredibly quickly and precisely without damaging the surface as it\'s non abrasive with it\'s circular motor movement. - Brand: Derwent - 500mAh lithium-ion battery - USB rechargeable - Includes 20 eraser refills, 10 large erasers and 10 extra fine erasers - Erases quickly and precisely - Circular motor movement and non abrasive - Function button to push on and off, letting your hand hold freely for maximum control