How to check internal resistance of 280ah LiFePo4 cells?

[JTrigger]

I found some videos showing how to do this using a resistor and multi meter, but it didn't say what resistor to use. Does it matter? Is there a better way? I want to see how well matched my cells are. They were supposed to come matched and balanced from the seller, but it appears 1 of them at least was not balanced with the rest as it had a slightly higher voltage 3.31v vs 3.28 on the other 7. Also when doing a serial charge at 24v that cell reached 3.6 when the others were only 3.34. I'm hoping I didn't get ripped off with a bad cell and it's just a little more charged and top balancing will fix it.