Here's an article on About.com:

Battery Testing, Maintenance And Myths

According to that article the voltage for load testing is dependent on electrolyte temp (see the chart in the article). If that voltage falls below the minimum, then according to that article, it is a bad battery.

For example, electrolyte at 0 degrees F, a good battery's voltage is not supposed to go below 8.5 volts. The highter the temp the higher the minimum voltage.