Some electronic foot files run on AA batteries, while others have built-in rechargeable batteries and include a charging dock or a USB charging cord for recharging.
Before use: briefly soak your feet in warm, sudsy water to soften the skin. During use: gently scrape or rub callused areas with the file or pumice. After use: rinse and dry your feet, and many instructions recommend applying a foot cream.
Electronic foot files commonly include extra or replacement roller heads and may come with a charging base or USB cord. Some kits list both coarse and fine roller heads for different levels of exfoliation.