Which Meter is Cheapest & Accurate for Internal Resistance Testing?

As @SammysHP says, you need a special/dedicated meter for this kind of measurement. A meter that can measure very low impedance and typically uses the 4 wire measurement method.
Here is a good discussion on the topic Lots of actually testing was done.

Here is another thread on BLF with some good info.

I got a couple of them. The BA1020 and the RC3563. I prefer the RC3563 because it is easier to calibrate.

Keep in mind that you will also need to get some good leads and it is easier if you get a cell holding fixture if you want to test cylindrical cells. They do sell kits such as this one.
https://shorturl.at/Ud3xd

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