Determine the no-load voltage of the battery or voltage regulator. Measure the output voltage of the battery or voltage regulator when there are no electronic devices attached. Conclude this is the no-load voltage. Use for this example a no-load voltage of 12 volts.
Determine the full-load voltage of the battery or voltage regulators. Connect all the electronic devices that the battery or voltage regulator must power to the battery or voltage regulator. Turn on the electronic devices. Now measure the battery or voltage regulator voltage. Conclude that this is the full-load voltage. Use for this example a full-load voltage of 11 volts.
Calculate the change in voltage. Subtract the no-load voltage obtained in Step 1 from the full-load voltage in Step 2. Conclude for this example that the change in voltage is 1 volt, since 12 minus 1 is 11.
Calculate the load regulation. Divide the change in voltage obtained in the previous step by the full-load voltage. For this example, calculate that the load regulation is 0.091 volts per volt, since 1 divided 11 is 0.091.
Calculate the percent load regulation. Multiply the load regulation in Step 4 by 100 percent. Conclude that the percent load regulation is 9.1 percent, since 100 multiplied by 0.091 is 9.1