Internal resistance is a critical parameter in batteries and capacitors, representing the opposition to the flow of electric current within the device. It's a key factor affecting the efficiency and performance of energy storage systems. Lower internal resistance allows for faster charging and discharging, higher power output, and reduced energy loss as heat. It's influenced by factors such as the materials used, the design of the device, and temperature. In electric vehicles, for example, batteries with low internal resistance are preferred for their ability to deliver high power and fast charging. Managing internal resistance is essential for optimizing the performance and longevity of energy storage devices.