Found two circuits online of almost same approach to measure internal resistance of a battery. Both the methods excite the battery at 50Hz using a square wave and AC voltage drop is measured across the battery (as per my understanding). And apparently, this voltage drop corresponds to the internal resistance of the battery

Method 1: https://www.eeweb.com/internal-resistance-tester-for-batteries/

Method 2: http://www.next.gr/meter-counter/Checker-Circuits/Internal-Resistance-Battery-Tester-l13989.html

In the method 1, it is mentioned that the voltage measured divided by 10 gives the internal resistance of the battery. And method 2 says, the internal resistance is 10 times the voltage measured. I request someone to please breakdown why it is so? whats happening in these circuits and what is the difference between them?And how reliable are these methods?Thanks in advance.