1. The problem statement, all variables and given/known data The potential difference across the terminals of a battery is 8.20 V when there is a current of 1.54 A in the battery from the negative to the positive terminal. When the current is 3.56 A in the reverse direction, the potential difference becomes 9.40 V. What is the internal resistance r of the battery? 2. Relevant equations V_ab = E - Ir 3. The attempt at a solution So I thought that it would make no difference if the charge was reversed. So I just plugged the values into the equations, so since I have two equations and two variables I could solve for r. 8.56 = E - 1.54r -> E = 8.56 + 1.54r 9.40 = E - 3.56r -> E = 9.40 + 3.56r - 0 = -.84 - 2.02r r = -.416 Obviously the resistance can't be negative. What am I doing wrong, does it have something to do with the reversing part of the problem?