You can definitely measure AC internal resistance. That's a standard thing with Li-ion cells, done at 1 kHz. In fact, I own a meter just for that purpose. But the values it produces are not the same as a proper DC internal resistance test, which requires pulling something resembling the cell's rated current for a brief time, and in the end, DC internal resistance is what matters when you're trying to turn an engine over with a starter motor, or get glow plugs to heat up, etc.I've heard about not only "small current" but "signals of different frequencies - to deeply analyze several parameters of the battery"
-Uwe-