When you purchase a 1.5V D-cell battery you expect the battery to operate at 1.5V. However, if you place a voltmeter across your new battery you will probably find that its original voltage is greater than 1.5V. This is because the manufacturer knows that when you draw current from their battery, some of its original energy is lost within the battery itself. The voltage that is left over for the rest of the circuit is known as the terminal voltage. How can we use this principle to test the performance of a battery?