Lithium-ion battery internal resistance test method:
According to the physical formula R=U/I, the testing equipment forces a large constant DC current (currently 40A-80A) through the lithium-ion battery for a short period of time (usually 2-3 seconds), measures the voltage across the lithium-ion battery at this time, and calculates the current internal resistance of the lithium-ion battery according to the formula.
1. Measure the open-circuit voltage of the battery: U1
2. A fixed-value resistor R is connected in parallel across the battery terminals to discharge it;
3. Measure the voltage across the lithium-ion battery during discharge: U2;
4. Calculate the battery's internal resistance: r = (U1 - U2) / (U2 / R)
For example, if a battery has an open-circuit voltage of 12V, and the voltage drops to 10V after a 10-ohm resistor is connected in parallel, then the internal resistance of the battery is: r=(U1-U2)/(U2/R)=(12-10)/(10/10)=2 ohms.
Generally, the higher the internal resistance (r) of a lithium-ion battery, the worse its load-carrying capacity. High-power batteries (such as rechargeable batteries) typically have very low internal resistance (r). Low-power batteries (such as 9V tandem batteries) typically have relatively high internal resistance.
