Ahh, now things are starting to make sense. Stupid marketing BS.
The higher level specs say it can sink/discharge "up to 1A" but if you dig into the manual far enough you find the discharge current is fixed at 1A and you have to add a resistor to reduce it, which is going to add that resistance onto the ESR measurement.
Which I'm guessing may push it out of the spec'ed range for ESR measurement if you add a resistor too large.
Also it seems to imply it needs to be a rechargeable batt as ESR is calculated on recharge.
And therefor perhaps non-rechargeable batts can't have their ESR measured by the 2281S-20-6 at all?
Can anyone recommend a similar piece of test gear around the 5k price range that can actually do battery simulation and create its own profiles from discharging the cell.
It's only for coin cells so doesn't need high voltages or high currents.