Battery Life - A Science Experiment

Which battery lasts the longest out of four different brands, Duracell, Energizer, Eveready and Rayovac?

We do suggest that further testing be done, due to a few errors made during the experiment. Some flashlights were accidentally dropped, which could have caused differences in the results. The expiration dates of the batteries were not all the same (there was a difference of a few months); so some batteries may not have been as "fresh" as the newer ones.