What is the term for the internal resistance found within a battery or power supply?

The term for the internal resistance found within a battery or power supply is "internal resistance." This resistance is a critical factor because it affects the efficiency of the battery and its ability to deliver power to an external circuit. Internal resistance arises from the materials and chemical processes within the battery, contributing to energy loss as heat when current flows.

When a battery is supplying power, the internal resistance reduces the effective voltage output compared to the open-circuit voltage. Understanding internal resistance is essential in assessing a battery's performance, especially in applications where high current is required. This knowledge aids in predicting how the battery will behave under varying loads and in optimizing power delivery for different devices.