Which of the following describes the internal resistance of a battery or cell?

The internal resistance of a battery or cell refers to the opposition provided by the battery to the flow of current internally when a voltage is applied. When current flows through a battery, it encounters resistance due to factors such as the chemical reactions within the battery, the physical layout of the internal components, and the materials used.

This internal resistance impacts the battery's performance, affecting how much voltage is delivered to an external circuit under load. When the internal resistance is high, it can lead to a significant voltage drop when current is drawn, which can reduce the efficiency and effectiveness of the battery. Therefore, the internal resistance is a crucial parameter that helps characterize the behavior of the battery during operation, particularly under load.

In contrast, the other options tackle different aspects of battery characteristics. The efficiency of a battery is influenced by internal resistance, but it is not exclusively defined by it. Voltage output is related to the terminal voltage when a battery is in use, which does not directly define the internal resistance. Similarly, stored energy is determined by the capacity of the battery and its voltage, but these concepts do not adequately capture what internal resistance measures.