To measure DC internal resistance with a multimeter, you first measure the unloaded voltage of the battery (v1), then the voltage under load (v2), and finally the resistance of the load (r1), which allows you to calculate the internal resistance using ISR = (V1 - V2)/ (V2/R1). There are two methods for measuring internal resistance: the AC method (AC-IR) and the DC. Measuring a lithium-ion cell's internal resistance is super strait forward. : all you have to do is get three readings and do a bit of math. First, record the cell's open-circuit voltage with no load attached. The determination of internal resistance is only possible in comparison with the value given by the manufacturer or obtained on a reference battery or a reference state of the very same battery (see. Therefore, it's important for manufacturers and battery researchers to measure values like DC internal resistance (DCIR) to identify low-quality batteries or to help study degradation behaviors. Source measure units (SMUs), like Keithley's 24xx Series Graphical Touchscreen SMUs with Test Script.
