Battery Internal Resistance
In this article, we will go over the battery internal resistance. All batteries have internal resistance to some degree because the elements it composed of are not 100% perfect conductors. Though the internal resistance may be low, always around 0.1Ω for an AA alkaline battery, and about 1Ω to 2Ω for a 9-volt alkaline battery, it can cause a noticeable drop in output voltage if a low-resistance load is attached to it.
This is easily understood if you still remember how voltage division works. The larger the resistance is, the more voltage gets allocated to that component. If a component has a very large impedance, that component will get most of the voltage, which comes from the battery, and vice versa. You should know that voltage gets allocated according to impedance values, so the impedance of the output device and the battery will always be divided up between each other.
Batteries with large internal resistance show poor performance in supplying high current pulses. This is because current is decreased with higher resistance. So the higher the internal resistance, the lower the current output ability. That’s why low internal resistance batteries are much better at supplying high current pulses.