1. The problem statement, all variables and given/known data 2. Relevant equations P=IV 3. The attempt at a solution I used the terminal voltage of battery B, that is I minus the voltage across the internal resistance of battery B from the e.m.f. of battery B, then I multiply it with the current which is 2.5A (calculated earlier) . But it should be just the e.m.f. of battery B multiply the current. Why the e.m.f. and not the terminal p.d.?