The battery internal resistance tester is a measuring instrument used to measure the internal resistance, voltage, and temperature of rechargeable batteries such as lead-acid batteries and lithium batteries to judge the health status of the battery. It can also be used as an instrument to measure the ESR parameters of electrolytic capacitors.
The internal resistance of a lithium battery can be measured using specialized equipment like battery analyzers or dedicated internal resistance meters. These devices apply a small known current to the battery and measure the voltage drop across it to calculate internal resistance.
Although batteries’ internal resistance would ideally be zero, internal resistance exists due to a variety of factors. Internal resistance increases as a battery degrades. On battery cell production lines, defective cells are detected by comparing the internal resistance of tested cells to that of known-good reference cells.
AC resistance meters (battery testers) apply a constant-current AC signal to the battery. This AC signal generally has a fixed frequency of 1 kHz, although some products allow the frequency to be varied.
One approach to calculating internal resistance involves the voltage drop method. Start by measuring the open-circuit voltage of the battery. Then, apply a known load (a resistor or device with a general resistance) to draw current from the battery. Measure the voltage across the battery terminals while the load is connected and drawing current.
Another aspect of Lithium Ion Battery internal resistance is polarization resistance. This resistance arises due to the electrochemical processes occurring within the battery during charge and discharge cycles.