Is battery internal resistance testing harmful to the battery itself?
It depends on your test method.
There are several methods: DC discharge method, AC test method, conductivity tester to measure battery internal resistance.
Using DC discharge, if the discharge current is small, the voltage decreases, the results are not allowed.
The discharge current large itself has certain damage to the battery. AC test method, because the battery internal resistance R includes complex, with the reaction time change of components, so the battery resistance measured by this method with the frequency of the exchange signal changes.
Measuring the internal resistance of the battery with the conductance tester is tested at a certain fixed frequency, that is, only one point is measured. When a constant current flows through the battery, the end voltage varies with time, the voltage changes at different times contain different components, so the battery resistance measured by this method varies with the frequency of the AC signal.
Because the battery is generated by internal chemical reaction of electricity, its internal resistance can not reflect the capacity of the battery itself, so the measurement of battery resistance is really meaningless.