A real battery has some internal resistance R_int in series with an ideal battery with an emf of V0. In an attempt to determine R_int and V0 of such a battery, the voltage across the battery terminals is measured with the battery disconnected from any circuit elements and is found to be 9.50 V. A resistor with R = 25Ω is then connected across the battery terminals, and the voltage across the terminals is found to be 8.10 V. Find the internal resistance of the battery. We give extra significant figures for the measured voltages so that the final answer will have two significant figures.