This resistance is designated by the letter "R" on circuit diagrams. In this article, we'll explore how to measure it in batteries and explain its impact.
To determine the battery's internal resistance, simply use a simple car headlight bulb. It's important that it's not an LED. A halogen bulb will work just fine.
It's known that a 60-watt light bulb consumes 5 amps of current. When the current is 100 amps, the internal "R" shouldn't consume more than 1 volt. Applying these values to a current of 5 amps, we find that the loss shouldn't be more than 0.05 volts. This can be expressed as (1 volt * 5 amps / 100 amps).
The resistance inside the battery should not be more than 0.05V / 5A = 0.01 Ohm.
Connect a multimeter in voltage mode and a light bulb in parallel to the battery. Observe the voltage. Turn off the light. Now observe the voltage. If it increases by 0.2 V (Re = 0.04 ohms) without this load, this means the battery is no longer usable. If it increases by 0.02 V, its internal resistance will be Re = 0.04 ohms, indicating it is fully functional.
With 100 amps, the loss will be 0.02 volts multiplied by 100 amps and divided by 5 amps. The result of these calculations is 0.4 volts.
