How Do You Calculate Battery Internal Resistance?
Most people think of a battery as a perfect voltage source. A new nine-volt battery supplies nine volts, regardless of the device it is powering. In reality, all batteries have internal resistance, which means that the battery’s voltage changes according to how much current it must deliver. At low current, the internal resistance of the battery is negligible. But in circuits that draw higher current from the battery, the decrease in voltage may be a problem. A battery’s ability to supply current can be determined by measuring its internal resistance and comparing this resistance to the overall resistance of the external circuit. Choose an appropriate value for the resistor to test the battery. Measurements will be more accurate if the value of the test resistor is not vastly different from the value of the battery’s internal resistance. A test resistor that is 10 or 20 times larger than the internal resistance is usually a good choice. Find an approximate value for the internal resista
