An electrochemical device that can preserve chemical energy and emit electric energy when required is referred to as a battery. The discharge capacity of a battery's enormous current is stronger when its internal resistance is smaller, which results in more electrical energy being dissipated. Every power supply includes some internal resistance. Naturally, in order to boost its carrying capacity, the internal resistance of the power supply must be held to a minimum.
The automobile battery has an internal resistance R and a load RL connected in series. The current flowing into R is equivalent to the load current. While the size of R remains constant, an increase in load current raises the current flowing through the internal resistance R and also the voltage at both ends of R. As a result, the voltage applied to the load RL decreases, and if this voltage drop is too high, RL may not operate effectively at the rated working voltage. Thus, it is crucial to keep the internal resistance of the battery as low as possible to prevent a large voltage drop at both ends of the internal resistance during overload driving. This will help ensure that the load RL operates correctly and efficiently.
With the passage of time, the internal resistance of the battery tends to increase, particularly in those batteries that are nearing the end of their useful life. Even though the battery voltage may initially remain high after being fully charged, the internal resistance gradually increases. Hence, when a high current load is applied, there is a voltage drop that occurs resulting in a reduction in the voltage between both ends of the load.