What does a built in rechargeable lithium battery mean?

A built-in rechargeable lithium battery refers to a battery that is integrated into a device and can be recharged using an external power source, such as a charger or USB port. Unlike removable batteries, this type is designed to stay within the device throughout its lifecycle. Lithium batteries are known for their high energy density, long lifespan, and lightweight properties, making them ideal for use in smartphones, laptops, and other portable electronics. The built-in design often contributes to a more compact and sleek device design.