No, the method is not correct at all. There are two ways. Apply a 1 kHz sine wave current to the battery. Measure V and I at 1kHZ to calculate R. The current should be small, but large enough to get a useable reading on your oscilloscope. Use AC coupling so you can see mV readings. Use a sense resistor on the low side of the battery to measure current.

The second way is to apply a low-duty cycle step current load. Measure the instantaneous voltage drop at the moment the step load turns on (you need an oscilloscope to do this). The load could be, say, C/10 or C/5. I usually do this with a function generator, a resistor, and a FET. The function generator turns the FET on. The resistor is attached so when the FET turns on, it becomes a load current to the battery.

No, the method is not correct at all (if you wish to duplicate manufacturer's specifications). There are two ways. Apply a 1 kHz sine wave current to the battery. Measure V and I at 1kHZ to calculate R. The current should be small, but large enough to get a useable reading on your oscilloscope. Use AC coupling so you can see mV readings. Use a sense resistor on the low side of the battery to measure current.

The second way is to apply a low-duty cycle step current load. Measure the instantaneous voltage drop at the moment the step load turns on (you need an oscilloscope to do this). The load could be, say, C/10 or C/5. I usually do this with a function generator, a resistor, and a FET. The function generator turns the FET on. The resistor is attached so when the FET turns on, it becomes a load current to the battery. The resistance is calculated using V/I = R, where V is the voltage change, and I is the step load current value.

If you measure the load voltage and no-load voltage with a slow instrument such as a battery analyzer, you will be measuring load droop caused by chemical rate effects at the anode and cathode. I guess this number could be meaningful, but it is not how the manufacturer measures internal resistance.