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# Why calling it 'impedance' ?

#### Externet

Greetings.
The cells forming a battery pack, and their internal characteristics, referred as 'impedance' instead of resistance. On day one I learned impedance is tightly tied to a frequency. Where is frequency present on direct current in order to use that term ? Seen used in several tutorials. Why ? Since when is that a proper way to refer to internal resistance ?

Pages 2-2 and 2-3 at

Battery internal resistance is in fact frequency and state-of-charge dependent. It's usually referred as impedance.

impedance is the combination of resistance and reactance(frequency-dependent part). It is not incorrect to refer to a wholly resistive parameter as impedance.

"Impedance" because something "impedes" the flow of current.
You could have said "resists" but that one's taken. So "resistance"
has its explicit dV/dI meaning, while "impedance" also includes
derivative and integral (inductor, capacitor) modes of "impeding".

Resistance is fine if the load is pure DC, but you need to use impedance if the load has transient or AC current components.

Impedence is where you get to use the pythagorean theorem from math class. Impedence is eqial to the hypotenuse of a right triangle with one leg equal to resistance and the other leg the reactance, either capacitive reactance or inductive reactance to alternating current. If the reactance is 0 then the impdance equals the resistance.

Thanks.
And... this internal 'impedance-named' for direct current cells in batteries; is when charging, standing-by, or discharging ?

Impedance can be measured in all battery operation states. We built battery testers that are able to superimpose AC current during charge, discharge and idle state performing impedance spectroscopy.