When the lights of an automobile are switched on, an ammeter in series with them reads 9.20 A and a voltmeter connected across them reads 12.40 V. When the electric starting motor is also turned on, the ammeter reading drops to 7.60 A and the lights dim somewhat. If the internal resistance of the battery is 53 mΩ and that of the ammeter is negligible, what is the emf of the battery?