In electrical terms, what does "internal resistance" indicate?

Internal resistance refers to the opposition to the flow of current within a battery itself. When a battery is in use, not all the energy produced by the chemical reactions inside is available to do external work; some energy is lost as heat due to this internal opposition. This energy efficiency loss is crucial in understanding how well a battery can perform when connected to a circuit, as higher internal resistance results in a lower voltage output and reduced performance under load.

While other factors like the capability to store charge and the physical size can influence battery performance, they do not directly define what internal resistance is. The voltage across an external load is affected by internal resistance but does not represent it. Therefore, understanding internal resistance is essential in evaluating a battery's efficiency and its ability to deliver power effectively.