1. The problem statement, all variables and given/known data The problem includes a graph. All I have is a current to external resistance graph, with 20 A coming at 10R of external resistance. I am to find the EMF and internal resistance of the battery. Here is the problem and my two attempts. http://1drv.ms/1LKbu5H 2. Relevant equations DeltaV = E - I * Rinternal 3. The attempt at a solution I included two of my attempts at a solution. In both cases I simplify the circuit such that I can find the R equivalent from Rinternal and Rexternal. While that can give me a ratio, I still don't know what the EMF of the battery is. One idea I had was to assume the max current on the graph (60 amps) is the max current the system can take. If this is correct, then I can reformulate the earlier formula to find a 'max possible I'. With this, I can find E in terms of Rin and I do find a solution, though I am highly unconfident if this is allowed.