USBC Battery Case Attachment For SONY Walkman WM-F404 3D printing, built-in screw connection, perfect compatibility with original machines. The lithium battery version has a capacity of 1800mAh and comes with a type c charging interface. It has perfect battery overcharge and over-discharge protection. The red light is on when charging and turns blue when fully charged. You can listen while charging. The built-in large-capacity original tantalum capacitor has a sweeter sound quality and more flexible bass. The screw packaging structure is used to facilitate self-replacement of the battery after battery attenuation in the future. Custom replacement batteries are provided at long-term cost price, so you no longer have to worry. We provide a charging cable