What is a common power source for portable computers?

The correct choice is internal battery packs, as they are a fundamental component of portable computers, allowing for mobility and use without being tethered to a power outlet. Internal battery packs provide the necessary power that enables laptops and other portable devices to operate independently. They are designed to be rechargeable, allowing users to work or use their devices on the go without worrying about a constant power supply.

Cabled connections to a power outlet do not align with the concept of portability, as they limit the mobility of the device. External solar panels could serve as an alternative power source, but they are not commonly used as a primary power source for most portable computers. Shared power from other devices is not a standard method for powering portable computers, as it involves complexities and compatibility issues that are typically not applicable in everyday use. Thus, internal battery packs are vital for the operational functionality and convenience of portable computers.