Datasheets for the cell
A 12 volt Li based battery is probably a LiFePo4 Battery and the IR of the whole battery will be skewed by the BMS system.
The best way to test the IR of cells is without any connections to them.
IR values are dependent on cell chemistry so the results can vary greatly.
Sure you can read IR (Internal resistance) on anything. Same as you can read IR on a capacitor in a circuit or the impedance of a choke but if they are in a circuit especially if they are powered up the readings are more than likely not valid.i thought i wouldbe able to read the IR ?