A car battery with a 12 V emf and an internal resistance of 0.050 is being charged with a current of 60 A. (a) What is the potential difference V across its terminals? Okay i have an equation that should work perfectly!! Points a and b are located at he terminals of the battery, thus the potential difference Vb-Va is the termian to terminal potential difference V across the battery, we see that: V = EMF - ir. r is the internal resitance of the battery, and they give me 60 amps as the current? V = (12V)-(60A)(.050) = 9V, which is wrong!