1. The problem statement, all variables and given/known data Two identical batteries of emf ε = 12 V and internal resistance r = 0.200 Ω are to be connected to an external resistance R, either in parallel or in series. If R = 2.00r Ω, what is the current i in the external resistance in the (a) parallel and (b) in the series arrangements? 2. Relevant equations 3. The attempt at a solution By symmetry, when the two batteries are connected in parallel the current i going through either one is the same. So from ε = ir + (2i)R with r = 0.200 Ω and R = 2.00r, we get ... etc. I have no idea what the above means. What is going on? While I appreciate the help, can you please give more than a sentence or two. I have found shortness = unhelpful response (not necessarily true, but there does seem to be a correlation).