You cannot simply model a battery as a capacitor with ESR, because it doesn´t behave like one.

 

yes i know as it has lot of other parameters for which i have other models already defined like internal temperature of a battery, internal resistance during load but as the battery is set to charging their is no load on it and it acts as a load on an alternator if i consider charge transfer resistance which is parallel to double layer capacitor then the voltage is same across both these elements and so my idea of calculating internal resistance would calculating the voltage drop across the resistance the moment the current crosses zero and then for a short run of a car the internal resistance would be remain constant or little bit varying because the emf of the battery will not change instantaneously

 

I don´t really understand what you mean, try using sentences and paragraphs please. You can calculate internal resistance as \(\frac{V_{1}-V_{2}}{I_{2}-I_{1}}\) for any two loads, with the resistance being positive for I1<I2