1. The problem statement, all variables and given/known data Circuit as shown below. At what voltage of E does the battery begin to charge? What percentage of the power is delivered to the 1R resistor by the voltage supply E when the charging current is zero? What is the current through the battery when E = 20V? 2. Relevant equations 3. The attempt at a solution I'm really not sure how to start with this one as there's nothing like this in the class notes as its an extension exercise the teacher set. I assume for the first part E obviously must be greater than 12V so I need to work out the effect of the resistors in the circuit?